Plumbing Systems Advanced

ADVANCED PLUMBING SYSTEMS

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PSD

136

Animal-careFacility PipingSystems

Continuing Education from Plumbing Systems & DesignKenneth G.Wentink, PE, CPD, and Robert D. Jackson

NOVEMBER/DECEMBER 2006

PSDMAGAZINE.ORG


INTRODUCTIONThis chapter discusses various piping systems uniquely associ-ated with the physical care, health, and well-being of labora-tory animals. Included are various utility systems for animal watering, water treatment, room and floor cleaning, equipment washing, cage flushing and drainage, and other specialized piping required for laboratory and experimental work within the facility. Other systems involved with general laboratory and facility work, such as those for compressed gases and plumbing, are discussed in their respective chapters.

GeNeRalIt is expected that a facility involved with long-term studies will have different operating and animal drinking-water qual-ity requirements than one used for medical research. For criti-cal studies, the various utility systems shall incorporate design features necessary to ensure reliability and provide a consistent environment. As many variables as are practical (or desirable) shall be eliminated to ensure the accuracy of the ongoing exper-iments being conducted. Regardless of the facility type, different users and owners have individual priorities based on experi-ences, operating philosophies, and corporate cultures that must be established prior to the start of the final design phase of a project.

CODes aND sTaNDaRDs1. The local codes applicable to plumbing systems must

be observed in the design and installation of ordinary plumbing fixtures and potable water and drainage lines for the facility.

2. 10-CFR-58 is the code (by the agencies of the federal government) for good laboratory practice for nonclinical laboratory studies.

3. 21-CFR-211, cGMP, requires compliance with FDA protocols for pharmaceutical applications.

4. NIH publication 86-23, Guide for the Care and Use of Laboratory Animals.

5. American Association for Accrediation of Laboratory Animal Care (AAALAC). Inspection and accreditation by the AAALAC is accepted by the NIH as assurance that the facility is in compliance with Public Health Services (PHS) standards.

aNImal DRINkING-WaTeR sysTemsThe purpose of the animal drinking-water system is to produce, distribute, and maintain an uninterruptible supply of drinking water with a specific and consistent range of purity to all ani-mals in a facility. There are two general types of systems: an automated central-distribution system and individual water bottles.

sysTem TypesThe great majority of animals used by laboratories for medical and product research are mice, rats, guinea pigs, rabbits, cats, dogs, and primates. Smaller animals and primates are kept in stacked cages, often on racks. Medium-sized animals, such as dogs, goats, and pigs, are kept in kennels or pens. Larger floor areas are required for barnyard animals such as cows. Water-ing can be done either by an automatic, reduced-pressure, cen-tral system, which pipes water from the source directly to each cage, kennel or pen; or by separate drinking bottles or watering devices manually placed in individual cages or pens.

Automated, Central Supply-and-Distribution SystemThe purpose of an automated, central, drinking-water supply system is to automatically treat and distribute drinking water. Ancillary devices are used to flush the system and maintain a uniform and acceptable level of purity.

The system consists of a raw or treated water source, a purifi-cation system, medicinal and disinfection injection equipment if necessary, pressure-reducing stations, and a distribution piping network consisting of a low-pressure room-distribution piping system and a rack-manifold pipe terminating in a drink-ing valve for each cage or pen for the animals. Also necessary is an automated flushing system for the room-distribution piping activated by a flush-sequence panel, and a monitoring system to automatically provide monitoring of such items as drinking-water pressure, flow, and possible leakage.

Animals in cages are kept in animal rooms. Cages are usually placed in multi-tiered, portable or permanent cage racks, which contain a number of cages. The cage rack has an integral piping system installed, called a rack manifold, that distributes the water to all cages. The rack manifold could be installed by the manufacturer or in the facility by operating personnel. The rack manifold receives its water from the room-distribution piping. The connection between the room-distribution piping and the rack manifold is made by means of a detachable recoil hose generally manufactured from Polypropylene (PP), nylon, or Eth-ylene-Propylene Diene Monomer (EPDM). This hose is flexible, generally 38 in. (12 mm) in size and coiled to conserve space. It will stretch to a length of about 6 ft 0 in. (2 m). Each end is pro-vided with a quick-disconnect fitting used to attach the hose to both the room-distribution piping and the rack manifold.

To maintain drinking-water quality, a method of flushing the room-distribution piping and the rack manifold shall be pro-vided. Ancillary equipment includes flushing and sanitizing systems to wash the recoil hose and the cage rack-piping inte-rior.

Water BottlesDrinking water bottles are individual units with an integral

drinking tube that are placed by hand on a bracket in each cage.

Animal-care FacilityPiping Systems

Reprinted from Pharmaceutical Facilities Plumbing Systems, Chapter 7: Animal-care Facility Piping Systems, by Michael Frankel. American Society of Plumbing Engineers.

Plumbing Systems & Design NOVEMBER/DECEMBER 2006 PSDMAGAZINE.ORG

CONTINUING EDUCATION


These bottles could be filled either by hand or automatically via a bottle filler.

Automatic bottle fillers should be considered to reduce the time necessary to fill bottles and minimize water spillage. Bottle fillers are available with manifolds to fit any size bottles. They can be supplied with purified water from a central water supply andwith separate, programmable proportionerscould acidify, chlorinate, and medicate the water as required. The bottle filler automates the filling procedure so that the bottles are correctly positioned during filling and stops the flow when the water reaches a predetermined level.

Flushing SystemIn order to maintain drinking-water quality, the drinking-water distribution system should be flushed periodically. This is accomplished by having the same drinking water that is nor-mally distributed to the animals flow through the piping system at an elevated flow rate, pressure, and velocity. The water is sent to drain and not recovered. This is initiated automatically at the drinking-water pressure-reducing station by the addition of separate regulating valves and pressure-regulating arrange-ments.

Different flushing arrangements are possible, depending on the cost, facility protocol, and purity desired. One method flushes only the main runs by the addition of a solenoid valve at the end of the main run and the provision of a return line to drain from this point. Another method is to flush the mains and the room-distribution piping by adding the solenoid valve at the end of each room-distribution branch with the return line to drain from each room. A third method flushes the entire system, including the rack manifold, by adding a solenoid valve on each cage connection to the room-distribution pipe, which flushes the recoil hose and the rack manifold.

It is accepted practice to replace all the drinking water in the room-distribution piping system at regular intervals, a minimum of twice daily. To approximate the amount of water in the pipe, allow 1 gal (4 L) for each 33 ft 0 in. (10 m) of pipe. General prac-tice is to flush the system with water at about 15 psi (90 kPa) at a rate of 15 gpm (60 L/min). If the drinking water is not purified, it is recommended that the piping be flushed at least twice daily for about 2 min. For purified water, flush once daily for about 1 min. Flushing can be done manually by means of a valve in the pressure-reducing station enclosure or automatically by the addition of a bypass and solenoid valve around the low-pres-sure assembly to the pressure-reducing station. The sequence and duration of the automatic flush cycle is controlled from a flush-sequencer panel.

DRINkING-WaTeR TReaTmeNT sysTemsThe purpose of the drinking-water treatment system is to remove impurities from the raw-water supply to achieve the water quality required by the animals in the facility. In addition, disinfectant and medica-tion can be added to the water during treatment if required.

sysTems DesCRIpTIONThere are no generally recognized and accepted standards for animal drinking-water quality. Purity and consistency requirements depend on the incoming water quality, the established protocol of the end user, the importance of either the initial or

the operating cost of the proposed system, the species of ani-mals housed in the facility, and the animal-housing methods. The overall objective is to eliminate as many variables as pos-sible for the entire period of time the studies or experiments are conducted.

The most often-used treatment for drinking water is reverse osmosis. Other possible treatment methods are distillation and deionization. A discussion of these purification methods appears in the chapter Water Systems.

Reverse OsmosisWhen a higher-quality water is required and other types of puri-fied water are not available in a facility, reverse osmosis (RO) is normally selected. Since the amount of water is usually small, a package type unit mounted on a skid is provided and connected directly to the water supply. The RO system is flexible and, when used in combination with DI water supply, will provide water that is virtually contamination free.

Disinfection and Medication of Drinking WaterDisinfection chemical mixtures are added to the animal drink-ing-water supply to eliminate and control bacterial contamina-tion in the central and room-distribution piping system. Medi-cation is added to conform with experimental protocols if nec-essary. These mixtures are usually introduced into the piping system by a self-contained, central, proportioning (injector) unit using facility water pressure. Medication is added to the drinking water using the same proportioning equipment that adds disinfectant. All equipment is available in a wide range of sizes and materials. A schematic detail of a typical central pro-portioner is illustrated in Figure 7-1.Chlorination Chlorination is a recognized biocidal treat-

ment that leaves a residual of chlorine in the entire central-dis-tribution system. Hyperchlorinated water is not as corrosive as acidified water and could be used with brass/copper distribution system components. Accepted practice is to provide a pH higher than 4, with a residual range of free chlorine between 5 and 12 ppm. Free chlorine in water dissipates in time with light, heat, and reaction with organic contaminants, making it ineffective when water bottles are used. Chlorine creates toxic compounds in reaction with some water contaminants and medications.Acidification Acidification has an advantage over chlori-

nation in that it is more stable and lasts longer in the system. The disadvantage is that corrosion-resistant materials must be used. The pH range should be between 2.5 and 3 in order to be effec-

Figure 7-1 Typical Central Proportioning Unit

NOVEMBER/DECEMBER 2006 Plumbing Systems & Design


tive. A pH lower than 2.5 will cause the water to become sour and the animals will not drink it. At a pH above 3, the mixture is not considered an effective germicide.

DRINkING-WaTeR sysTem COmpONeNTs aND seleCTION

pRessURe-ReDUCING sTaTIONThe pressure-reducing station reduces the normal pressure of the raw-water supply to a level required for the animal-room drinking-water distribution system. As an option, a secondary system can be added to provide a higher pressure in the room-distribution system for flushing.

The pressure and flow rate depend on the type and number of animals to be supplied. Also usually included are a 5- water filter, a pressure gauge, and a backflow preventer. Timing devices that automatically control flushing duration are con-trolled by a remote flush-sequencer panel, which controls all flushing sequencing operations. The recommended pressures for animal-room piping distribution to various animals are as follows:

Small animals, such as Rats and mice 3-5 psig (20.4-34 kPa)Primates 3-5 psigDogs and cats 3-5 psigSwine and piglets 6-12 psig (41-81.6 kPa)

The secondary pressure-reducing assembly used to provide automatically room-distribution pipe-flushing water operates at a pressure of 15 psig (102 kPa). This assembly is installed as a bypass around the low-pressure assembly. Manual operation at a lower cost could also be provided. This additional pressure for a short period of time will not cause the animals any difficulty if they decide to drink during the flushing cycle.

One pressure-reducing station can be connected to as many as 35 interconnect stations to small animal-rack manifolds, often referred to as drops. This allows 1 station to control more than 1 animal room.

The pressure-reducing station is a preassembled unit com-plete with all the various valves, fittings, and reducing valves required for a specific project. All the components are installed in a cabinet, which requires only mounting and utility connec-tions.

DRINkING ValVesDrinking valves are used by the animals to obtain water from the distribution-system piping. An internal mechanism keeps the valve normally closed; the animal drinking from the valve must open it by some action, such as moving the entire valve or operating a small lever inside the body of the valve with the tongue. Many different kinds of valve are available to supply any type of animal that may be kept in the facility. The valves can be mounted on cages, on the rack manifold, or on the walls of pens and kennels at varying heights with the use of special brackets.

aNImal-RaCk maNIfOlD CONfIGURaTIONsThe configuration of the piping on the animal rack plays an important part in the effectiveness and efficiency of the filling and flushing of the drinking-water system. The two most often-used configurations are the reverse S and the H.

The reverse S, illustrated in Figure 7-2, is the most often-used configuration. It has two basic styles based on the valve location in the flush drain line. One style has a supply control valve at the top and the other has a drain valve at the bottom. Either location is acceptable, with the deciding factor being the ease of operating the valve where the rack is installed. This configuration has the advantage of eliminating dead legs and offers more convenience to facility personnel when they fill the piping after washing. The vent is a manually operated air bleed used when the cage rack is reconnected to the room-distribution pipe. It is opened until water is discharged, thereby eliminating any air pockets in the manifold. This manifold style provides a positive exchange of water during flushing with a minimum usage of time and water.

Figure 7-2 Reverse S Configuration Watering Manifold

Figure 7-3 Typical Room Distribution, On-Line, Rack Manifold Flushing System

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CONTINUING EDUCATION: Animal-care Facility Piping Systems


This configuration is used far more than any other manifold style. It is easily converted to automatic flushing by the installation of solenoid devices on the valve. It is recom-mended when micro-isolator cage systems are installed. The complete, on-line, rack-manifold flushing system is illustrated in Figure 7-3. This cage system has the advan-tage of the complete isolation of individual cages, with the accompanying capability for additional flushing and disinfection of the piping system.

One variation of the reverse S is the standard S, illustrated in Figure 7-4. This configuration has the advantage of com-plete on-line flushing and lower initial cost of the manifold. Disadvantages are the need for extra supports on the cage rack and the need for venting to be done man-ually or by the animals after being placed in service. This configuration is no longer recommended.

The H style, illustrated in Figure 7-5, although rigidly installed and with positive venting, is not suitable for on-line flushing. Because of this, it is rarely used except for larger ani-mals, which will consume all the water in the rack piping mani-fold.

The most common piping materials are CPVC and 304L stain-less steel. CPVC conforms to ASTM D 2846, is 0.875 outside diameter (OD) with 0.188 in. minimum wall thickness. Joining process is done with solvent cement socket joints. The drinking valves are installed with a proprietary, drilled and tapped fit-ting. The 304L stainless steel tubing is 0.50 OD with a 0.036 in. minimum wall thickness. Fittings are made with O-ring joints and socket fittings or compression type fittings. The mounting of both pipe materials is accomplished by the use of 304 SS stain-less-steel clamps and fasteners.

sysTem sIzING meThODsThe water consumption of small animals in cages is very low. It is also probable that the animal room will not be used to full capacity. Because of this low consumption flow rate, the flush-ing-water flow rate of the system is the critical factor in sizing the piping. Typically, the animal-room piping distribution net-work is a header uniformly sized at in. (50 mm) throughout the animal room.

The pipe sizes in other areas of the animal facility are determined based on the requirements of maximum flow rate at the necessary pressure to supply the flush-ing velocity. Maximum flow rate depends on the flush sequencing, and the pressure drop depends on overcoming pressure loss through the equipment connected to the branch being sizedsuch as pressure-reducing stations, solenoid valves, and recoil hosesand friction loss through the piping network. Allowance must be made to provide a sufficiently high flow rate and water velocity to efficiently provide the flushing action desired.

CleaNING aND DRaINaGe sysTems aND pRaCTICes

GeNeRalKeeping the animal rooms and cages

clean is an extremely important facet of facility practice. The cleaning of the animal room is accomplished either by sponging the walls, floors, and ceiling or by hosing down the room. Cage racks can be cleaned by washing them with a hose or by placing them in a large washing machine. Cages are cleaned in a cage washer. Pens and kennels are hosed down. Floors in pens are cleaned with hoses and the bedding with feces is pushed into trenches with floor drains.

In specialized areas, such as holding or isolation rooms where only small animals are kept, it is common practice to have per-manent cage racks or have the portable racks remain in the animal room. The litter is put into bags and brought to other areas for disposal. The cage racks are manually wiped down and no rack washer is required. A sink is usually provided in the animal room for the convenience of the cleaning personnel. Individual water bottles, if provided, could be washed in the sink. The cages are removed and washed separately in a cage washer. This type of animal room usually does not require a floor drain if the entire room will be sponged down. If hosing is practiced, a floor drain is required.

Rabbits and guinea pigs have a tendency to spray urine and feces. This requires that the racks be hosed down in the room. A wash station with a hose reel and detergent injection capability to hose down the cage racks and the room itself is usually placed in individual rooms. Citric acid is often used as a cleaning agent for rabbits.

hOse sTaTIONsHose stations usually consist of a mixing valve with cold water and steam to make hot water or hot water alone, a length of flex-ible hose, and an adjustable spray nozzle. Hot and cold water are also used. It can be exposed or provided with an enclosure when an easily cleaned surface is required.

CleaNING-aGeNT sysTemsCleaning agents are used to clean and/or disinfect the walls, ceiling, and floor of a room and to add agent to the cage wash water. When used to clean rooms, the equipment used for this purpose is commonly called a facility detergent system. When used to add agent to the cage washing water it is often called a cage-washing detergent system. These are separate systems and are not capable of providing agent to each other.

Figure 7-4 Standard S Configuration Manifold

Figure 7-5 Standard H Configuration Manifold



A single-station detergent-dispensing system is used when rooms are cleaned with mops or squeegees. It consists of a wall-mounted unit having a holder for detergent concentrate and an injector unit. A container filled with detergent concentrate is placed in the holder and is used to supply agent to the injector that dispenses a metered amount of agent when a hose bibb is opened to fill the pail or container. These rooms usually have sinks and mop racks inside to be used only for these rooms. A typical schematic detail of a single-station detergent system is illustrated in Figure 7-6.

When used to supply a single or multiple-spray hose for cleaning floors and walls, a central system could be installed to supply several rooms within a facility by means of a detergent pump that dispenses agent. A 55-gal drum of agent should be used to reduce the number of times the

supply has to be changed. A typical central-supply deter-gent-dispensing system is illustrated in Figure 7-7.

The cage-washing detergent system is usually located in the wet area of the cage-washing facility and, with the use of a detergent pump, could be used as a central system to supply cage and bottle washers. A typical schematic detail of a cage-washing system is illustrated in Figure 7-8.

It is common practice to have a central system or a wall-mounted cleaning-agent dispenser unit along with the hose station. Separate, portable units could be used when cross contamination between animal rooms is a consideration. A typical, wall-mounted, cleaning-agent system consists of separate water and cleaning-agent tanks; a water pump; and a special, coaxial hose that sprays a proportioned mix-ture of the water and cleaning agent. Compressed air is often used to provide pressure.

CaGe-flUshING WaTeR sysTemThe removal of animal waste from cages can be done by sev-eral methods. One method removes the waste along with the bedding at the time cages are removed from the animal room to be washed. Another method uses an independent rack-flush system to automatically remove animal waste from cages on racks while the animals and cages remain in the animal room.

The independent rack flush is a separate system that uses chlorinated water automatically distributed to each animal room. The cages and racks are constructed so that

the animal droppings fall through the cage floor onto a sloping pan below each tier of cages. Each tier is cascaded at the end onto the sloping pan below. Eventually, the lowest pan spills into a drain trough in the animal room. The flushing schedule is decided by facility personnel.

The water supply could be a reservoir placed on the rack that is filled with water and automatically discharged onto the pans at preset intervals. These preset intervals are determined based on experience and generally range from once to three times daily. Another method uses a solenoid valve to automatically discharge water onto the pans; the valve is sequenced by a timer set to alternate fill and dump cycles. The timer could be either

Figure 7-6 Single-Station Detergent System

Figure 7-8 Typical Cage-Washing Detergent System

Figure 7-7 Central-Supply Detergent System




centrally located or installed separately in each animal room. Larger cages, such as those for primates, are usually stacked no more than two cages high. Current practice is to have these cages manually cleaned by personnel who hose down the pans directly into floor or wall troughs.

Water is supplied to each cage rack by means of a recoil hose, which has a different quick-disconnect end than that of the drinking water recoil hose to avoid cross connection. Refer to Figure 7-9 for a detail of a typical cage-rack utility connection arrangement.

sOlID-WasTe DIspOsalSolid waste consists of bedding, feces, animal carcasses, and other miscella-neous waste, including straw and sawdust used for larger farm animals. Bedding comprises the largest quantity of this solid waste. It is necessary to determine the quantity of bedding before a decision can be made as to the most cost-effective method to dispose of it.

Bedding can be disposed of by incin-eration, as regular garbage, or into the sewer system. Incinerators are costly, require compliance with many regulatory agencies and multiple permits, and often result in objections from adjoining prop-erty owners. Incineration is the preferred method of disposing of carcasses and large quantities of contaminated waste. Carcasses could also be autoclaved and

disposed of as regular garbage. Regular gar-bage disposal is the most common method of disposal. It involves collecting, moving, and storage of the waste into large containers until regular garbage collection is made. This is very labor intensive.

Discharge into the drainage system must first be accepted by the local authorities and responsible code officials. This requires the bedding to be water soluble, that it shall not float, and provision be made to thoroughly mix the bedding with water. This mixture is called a slurry. Experience has shown, if done prop-erly, discharge into an adequately sized drain lineminimum size 6 in. (150 mm)has caused no problems, since the effluent has the same general characteristics of water.

A self-contained waste-disposal system is available that is capable of disposing of animal bedding and waste. The system consists of a pulping unit to grind the waste into a slurry and sanitize it, a water extractor to remove most of the water from the slurry, and the interconnecting piping system that transports the slurry from the pulper to the extractor and recirculates the water removed from the extractor back to the pulping unit for reuse. The solid waste is removed as garbage. Manufac-turers are available for assistance in the design and equipment selection for this specialized

system. The system has the advantages of reducing water use, reducing operating costs by eliminating the handling of the waste by operating personnel, compacting the waste to about 20% of the space required for standard garbage not compacted, and reducing the possibility of contamination by isolation of the disposal equipment. The disadvantage is its high initial cost.

Figure 7-9 Typical Cage-Rack Utility Connections

Figure 7-10 Typical Waste-Disposal System



This system could consist of single or multiple units of dif-ferent capacities. It requires water intermittently for pulping at the rate of about 10 to 30 gpm (63 to 190 L/min). Hose bibbs should be installed for washdown. The pipe should be sized for a maximum velocity of 8 fps (1.75 m/s), with typical slurry lines ranging between 2 and 4 in. (50 and 200 mm) and return lines generally 2 in. (50 mm) in size. The extractor discharges into a drain that should be 4 or 6 in. (100 or 150 mm) depending on the flow. A typical schematic diagram of a multiple installation is illustrated in Figure 7-10.

ROOm-WasTe DIspOsalThe rooms in which animals are kept must be designed to allow proper drainage practices and in accordance with the antici-pated cleaning procedures of the facility. Floor drains, drainage trenches (or troughs) at room sides, adequate and consistent floor pitch to drains or troughs, and floor surfaces are all impor-tant considerations.

There are several considerations to be taken into account in locating floor drains. Experience has shown that placing drains in the center of a room is not acceptable because it is difficult to hose solids down a drain in this location. Another reason is that the floor must be pitched to the drain and if a cage rack is defective, it should roll to the side of the room. The best loca-tion is in a corner or at the side. Floor drains without troughs can be considered if the floors will only be squeegeed rather than hosed down. They should also be considered in contagious areas where contamination between rooms must be avoided. Gratings must have openings smaller than the wheels of racks or cages.

In rooms where washdown and cage-rack flushing are expected, the provision of a floor trough should be consid-ered. Troughs are often provided at opposite ends of the room to minimize the amount of floor drop due to pitch. Accepted practice uses a minimum floor pitch of 18 in./ft of floor run. The floor is pitched to the troughs to facilitate cleaning and also to provide an easy method to dispose of waste generated from the rack-flush system. It is common practice to provide an auto-matic or manual trough-flushing system with nozzles or jets to wash down the trough sides and eliminate as much of the con-tamination remaining in the trough as possible. Wall troughs, similarly to roof gutters, are located at a higher elevation. This type of trough arrangement is sometimes provided in addition to or in lieu of floor troughs if the arrangement of elevated cages and racks make it an effective drainage method. Experience has shown that prefabricated drain troughs in floors are preferred over those built on the wall as part of the architectural construc-tion.

The floor troughs are drained by means of a floor drain placed in a low point at one end. The troughs are usually pitched at in./ft of run to the drain. The drain should be constructed of acid-resistant materials and have a grate that can be easily removed. For small animal rooms where bedding is not disposed of in the room, a 4-in. (100-mm) drain is considered adequate. In most other locations, it is recommended that a 6-in. (150-mm) drain be provided. A flushing-rim type drain should be considered to flush all types of waste into the drainage system.

Floor drains should have the capability of being sealed by the replacement of the grates with solid covers during periods when the room may not be in service.

eqUIpmeNT WashINGMost facilities contain washing and sanitizing machines to wash cages, cage racks, and bottles, if used. There are two commonly used types of cage washer: the batch type and conveyer (tunnel) type. Batch washers require manual loading and unloading and are used where a small number of cages and racks are washed. The conveyer type is similar to a commercial dishwasher, where the cages and racks are loaded on a conveyer and automatically moved through the machine for the washing and sanitizing cycles.

eqUIpmeNT saNITIzINGMaintaining drinking-water quality requires that the recoil hoses and rack manifolds be not merely washed but internally sanitized. This is most often done at the same time the cages are washed. Separate rack-manifold and recoil-hose flush stations are available for this purpose and are usually installed in the cage-wash area. Washing can be done manually or automati-cally. The hoses are flushed for 1 to 2 min with 4 gpm (16 L/min) of water. Chlorine is injected into the water by a chlorine-injec-tion station (proportioner) set to deliver 10 to 20 ppm into the flush water. Ten scfm of oil-free compressed air at 60 psig is blown through the hoses to dry them. If chlorine is used as a disinfectant, a contact time of 30 min is recommended before evacuation and drying.

Periodic sanitizing of the room-distribution piping system is required for maintaining good water quality. Sanitizing is done prior to system flushing. To accomplish this, a portable sanitizer is used to manually inject a sanitizing solution directly into the piping system. In order to do this, an injection port is required at the inlet to the pressure-reducing station. The portable sani-tizer usually consists of a 20-gal (90-L) polyethylene tank with a submersible pump inside and a flexible hose used to connect the tank to the injection port. The disinfecting solution is a mix-ture of chlorine and water with 20 ppm of chlorine. The mixture should maintain a contact time in the piping of 30 to 45 min.

DRaINaGe-sysTem sIzINGAs mentioned previously, for individual animal rooms where bedding is not disposed of in the drainage system, a 4-in. drain is acceptable. In general, a 6-in. drain is considered good practice. The size of the drainage system piping should be a minimum of 6 in., with a -in. pitch when possible and the piping sized to flow to 23 full in order to accommodate unexpected inflow.

mONITORING sysTemsThe monitoring of various animal-utility systems is critical to keep within a range of values consistent with the protocol of the experiments being conducted at the facility. This is accom-plished by a central monitoring system that includes many mea-surements from HVAC and electrical systems. For the animal drinking-water system, parameters such as water pressure, flow rates, leakage, pH, and temperature in various areas of the facil-ity are helpful for maintenance, monitoring, and alarms.

sysTems DesIGN CONsIDeRaTIONsThe amount of exposed piping inside any animal room should be minimized. The exception is the animal drinking-water system, which is usually exposed on the walls of the room. This piping should be installed using standoffs to permit proper cleaning of the wall and around the pipe.

The piping material used for all systems should be selected with consideration given to the facility cleaning methods and




type of disinfectant. Where sterilization is required and cleaning very frequent, stainless-steel pipe should be considered.

If insulation is used on piping, it should be protected with a stainless steel jacket to permit adequate cleaning.

Pipe penetrations should be sealed with a high-grade, imper-vious, and fire-resistant sealant. Escutcheons should not be used because they allow the accumulation of dirt and bacteria behind them.



CONTINUING EDUCATION

PSD

136

Continuing Education from Plumbing Systems & DesignKenneth G.Wentink, PE, CPD, and Robert D. Jackson

CE QuestionsAnimal-care Facility Piping Systems (PSD 136)

About This Issues ArticleThe November/December 2006 Continuing Education

article is Animal-care Facility Piping Systems, Chapter 7 of Pharmaceutical Facilities Plumbing Systems by Michael Frankel. This chapter discusses the various piping systems uniquely associated with the physical care, health, and well-being of laboratory animals. Included are utility systems for animal watering, water treatment, room and floor cleaning, equipment washing, cage flushing and drainage, and other specialized piping required for laboratory and experimental work within the facility.

You may locate this article at www.psdmagazine.org. Read the article, complete the following exam, and submit your answer sheet to the ASPE office to potentially receive 0.1 CEU.

1. What comprises the largest solid waste item from animal cages? a. bedding, b. feces, c. carcasses, d. miscellaneous waste

. This chapter discusses various piping systems uniquely associated with the physical care, health, and well-being of ___________.a. laboratory workers, b. laboratory animals,

c. animal watering, d. cage cleaning

. A single-station detergent-dispensing system is used when rooms are ___________.a. hosed downb. cleaned with mops or squeegeesc. cleaned with steamd. none of the above

. To maintain drinking water quality, ___________.a. a water purification system must be designedb. the water system must be allowed to run continuouslyc. there must be chlorine injectiond. the drinking water distribution system must be flushed

periodically

. Floor drains should not be placed ___________ where animals are kept.a. under cages in roomsb. in the center of the roomc. at the back edge of cages in roomsd. none of the above

. A pulping unit is used to ___________.a. separate water from solid wasteb. determine the pH of the wastec. determine the temperature of the wasted. grind the waste into a slurry

. 10-CFR- ___________.a. is the federal code that must be followed when keeping

animals for researchb. requires compliance with FDA protocols for

pharmaceutical applications

c. is the guide for the care and use of laboratory animalsd. is the code for good laboratory practice for non-clinical

laboratory studies

. Select the true statement below.a. There are no generally recognized and accepted

standards for animal drinking water.b. Drinking valves are not used by animals to obtain water

from the distribution system.c. Water pressure, minimum and maximum, for the

various animals to be served is mandated in the plumbing code.

d. Reverse osmosis (RO) systems are inappropriate for animal drinking water systems.

. The recommended water pressure for dogs and cats is ___________.a. 612 psig, b. 20.434 kPa,

c. more than for rats and mice, d. none of the above

10. What flow rate and pressure of oil-free air is used to dry the interior of hoses?a. 5 scfm at 30 psigb. 10 scfm at 30 psigc. 5 scfm at 60 psigd. 10 scfm at 60 psig

11. What type of piping material should be used on systems that require frequent sterilization?a. cast ironb. copperc. galvanizedd. stainless steel

1. The water consumption of small animals in cages is ___________.a. based on a flushing system to maintain fresh water in

the piping at all timesb. established by experiencec. very lowd. none of the above

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Appraisal QuestionsAnimal-care Facility Piping Systems (PSD 136)

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NOVEMBER/DECEMBER 2006 Plumbing Systems & Design 11


PSd

143

Recirculating DomesticHot WaterSystemsContinuing education from Plumbing Systems & Design

Haig demergian, Pe, CPd

DECEMBER 2007

PSDMAGAZINE.ORG


INTRODUCTIONIt has been determined through field studies that the correct sizing and operation of water heaters depend on the appropriateness of the hot water maintenance system. If the hot water maintenance system is inadequate, the water heater sizing criteria are wrong and the temperature of the hot water distributed to the users of the plumb-ing fixtures is below acceptable standards. Additionally, a poorly designed hot water maintenance system wastes large amounts of energy and potable water and creates time delays for those using the plumbing fixtures. This chapter addresses the criteria for estab-lishing an acceptable time delay in delivering hot water to fixtures and the limitations of the length between a hot water recirculation system and plumbing fixtures. It also discusses the temperature drop across a hot water supply system, types of hot water recircula-tion system, and pump selection criteria, and gives extensive infor-mation on the insulation of hot water supply and return piping.

BaCkgROUNDIn the past, the plumbing engineering community considered the prompt delivery of hot water to fixtures either a requirement for a project or a matter of no concern. The plumbing engineers decision was based primarily on the type of facility under consideration and the developed length from the water heater to the farthest fixture. Previous reference material and professional common practices have indicated that, when the distance from the water heater to the farthest fixture exceeds 100 ft (30.48 m) water should be circulated. However, this recommendation is subjective, and, unfortunately, some engineers and contractors use the 100-ft (30.48-m) criterion as the maximum length for all uncirculated, uninsulated, dead-end hot water branches to fixtures in order to cut the cost of hot water distribution piping. These long, uninsulated, dead-end branches to fixtures create considerable problems, such as a lack of hot water at fixtures, inadequately sized water heater assemblies, and thermal temperature escalation in showers.

The 100-ft (30.48-m) length criterion was developed in 1973 after the Middle East oil embargo, when energy costs were the paramount concern and water conservation was given little consideration. Since the circulation of hot water causes a loss of energy due to radiation and convection in the circulated system and such energy losses have to be continually replaced by water heaters, the engineering community compromised between energy loss and construction costs and developed the 100-ft (30.48-m) maximum length criterion.

LeNgTh aND TIme CRITeRIaRecently, due to concern about not only energy conservation but also the extreme water shortages in parts of the country, the 100-ft (30.48-m) length criteria has changed. Water wastage caused by the long delay in obtaining hot water at fixtures has become as critical an issue as the energy losses caused by hot water temperature maintenance systems. To reduce the wast-ing of cooled hot water significantly, the engineering com-munity has reevaluated the permissible distances for uncir-

culated, dead-end branches to periodically used plumbing fixtures. The new allowable distances for uncirculated, dead-end branches represent a trade-off between the energy utilized by the hot water maintenance system and the cost of the insulation, on the one hand, and the cost of energy to heat the excess cold water makeup, the cost of wasted potable water, and extra sewer surcharges, on the other hand. Furthermore, engineers should be aware that various codes now limit the length between the hot water maintenance system and plumbing fixtures. They also should be aware of the potential for liability if an owner questions the adequacy of their hot water system design.

What are reasonable delays in obtaining hot water at a fixture? For anything beside very infrequently used fixtures (such as those in industrial facilities or certain fixtures in office buildings), a delay of 0 to 10 sec is normally considered acceptable for most residential occupancies and public fixtures in office buildings. A delay of 11 to 30 sec is marginal but possibly acceptable, and a time delay longer than 31 sec is normally considered unacceptable and a significant waste of water and energy. Therefore, when designing hot water systems, it is prudent for the designer to provide some means of getting hot water to the fixtures within these acceptable time limits. Normally this means that there should be a maximum distance of approximately 25 ft (7.6 m) between the hot water maintenance system and each of the plumbing fixtures requiring hot water, the distance depending on the water flow rate of the plumbing fixture at the end of the line and the size of the line. (See Tables 1, 2, and 3.) The plumbing designer may want to stay under this length limita-tion because the actual installation in the field may differ slightly from the engineers design, and additional delays may be caused

Recirculating Domestic Hot Water Systems

Reprinted from Domestic Water Heating Design Manual, Second Edition, Chapter 14: Recirculating Domestic Hot Water Systems. American Society of Plumbing Engineers , 2003.

2 Plumbing Systems & Design DECEMBER 2007 PSDMAGAZINE.ORG

CONTINUINg eDUCaTION

Table 1 Water Contents and Weight of Tube or Piping per Linear FootNominal Diameter

Copper Pipe Type L

Copper Pipe Type M

Steel Pipe Schedule 40

CPVC Pipe Schedule 40

(in.)aWater

(gal/ft)Wgt.

(lb/ft)Water

(gal/ft)Wgt.

(lb/ft)Water

(gal/ft)Wgt.

(lb/ft)Water

(gal/ft)Wgt.

(lb/ft) 0.012 0.285 0.013 0.204 0.016 0.860 0.016 0.210 0.025 0.445 0.027 0.328 0.028 1.140 0.028 0.290

1 0.043 0.655 0.045 0.465 0.045 1.680 0.045 0.4201 0.065 0.884 0.068 0.682 0.077 2.280 0.078 0.5901 0.093 1.14 0.100 0.940 0.106 2.720 0.106 0.710

a Pipe sizes are indicated for mild steel pipe sizing.

Table 1(M) Water Contents and Weight of Tube or Piping per MeterNominal Diameter

Copper Pipe Type L

Copper Pipe Type M

Steel Pipe Schedule 40

CPVC Pipe Schedule 40

(mm)aWater

(L)Wgt. (kg)

Water (L)

Wgt. (kg)

Water (L)

Wgt. (kg)

Water (L)

Wgt. (kg)

DN15 0.045 0.129 0.049 0.204 0.061 0.390 0.061 0.099DN20 0.095 0.202 0.102 0.328 0.106 0.517 0.106 0.132DN25 0.163 0.297 0.170 0.465 0.170 0.762 0.170 0.191DN32 0.246 0.401 0.257 0.682 0.291 1.034 0.295 0.268DN40 0.352 0.517 0.379 0.940 0.401 1.233 0.401 0.322

a Pipe sizes are indicated for mild steel pipe sizing.


by either the routing of the pipe or other problems. Furthermore, with the low fixture discharge rates now mandated by national and local laws, it takes considerably longer to obtain hot water from non-temperature maintained hot water lines than it did in the past, when fixtures had greater flow rates. For example, a public lavatory with a 0.50 or 0.25 gpm (0.03 or 0.02 L/sec) maximum discharge rate would take an excessive amount of time to obtain hot water from 100 ft (30.48 m) of uncirculated, uninsulated hot water piping. (See Table 3.) This table gives conservative approximations of the amount of time it takes to obtain hot water at a fixture. The times are based on the size of the line, the fixture flow rate, and the times required to replace the cooled off hot water, to heat the pipe, and to offset the convection energy lost by the insulated hot water line.

ResULTs Of DeLays IN DeLIveRINg hOT WaTeR TO fIxTUResAs mentioned previously, when there is a long delay in obtaining hot water at the fixture, there is significant wastage of potable water as the cooled hot water supply is simply discharged down the drain unused. Furthermore, plumbing engineers concerned about total system costs should realize that the cost of this wasted, previously heated water must include: the original cost for obtaining potable water, the cost of previously heating the water, the final cost of the waste treatment of this excess potable water, which results in larger sewer surcharges (source of supply to end disposal point), and the cost of heating the new cold water to bring it up to the required tem-perature. Furthermore, if there is a long delay in obtaining hot water at the fixtures, the faucets are turned on for long periods of time to bring the hot water supply at the fixture up to the desired tempera-

ture. This can cause the water heating system to run out of hot water and make the heater sizing inadequate, because the heater is unable to heat all the extra cold water brought into the system through the wastage of the water discharged down the drain. In addition, this extra cold water entering the hot water system reduces the hot water supply tempera-ture. This exacerbates the problem of insufficient hot water because to get a proper blended temperature more lower temperature hot water will be used to achieve the final mixed water temperature. (See Chapter 1, Table 1.1.) Additionally, this accelerates the downward spiral of the temperature of the hot water system.

Another problem resulting from long delays in getting hot water to the fixtures is that the fixtures operate for longer than expected periods of time. Therefore, the actual hot water demand is greater than the demand normally designed for.

Therefore, when sizing the water heater and the hot water piping distribution system, the designer should be aware that the lack of a proper hot water maintenance system can seriously impact the required heater size.

meThODs Of DeLIveRINg ReasONaBLy PROmPT hOT WaTeR sUPPLy Hot water maintenance systems are as varied as the imagina-tions of the plumbing engineers who create them. They can be grouped into three basic categories, though any actual installation may be a combination of more than one of these types of system. The three basic categories are1. Circulation systems.2. Self-regulating heat trace systems.3. Point-of-use water heaters (include booster water heat-

ers).

CirCulation SyStemS for CommerCial, induStrial, and large reSidential ProjeCtSA circulation system is a system of hot water supply pipes and hot water return pipes with appropriate shutoff valves,

balancing valves, circulating pumps, and a method of controlling the circulating pump. The diagrams for six basic circulating systems are shown in Figures 1 through 6.

Self-regulating Heat traCeOver approximately the last 20 years, self-regulating heat trace has come into its own because of the problems of balancing circulated hot water systems and energy loss in the return piping. For further discussion of this topic, see Chapter 15.

DECEMBER 2007 Plumbing Systems & Design 3

Table 3 Approximate Time Required to Get Hot Water to a FixtureDelivery Time (sec)

Fixture Flow Rate (gpm) 0.5 1.5 2.5 4.0

Piping Length (ft) 10 25 10 25 10 25 10 25

Copper in. 25 63a 8 21 5 13 3 8 Pipe in. 48a 119a 16 40a 10 24 6 15Steel Pipe in. 63a 157a 21 52a 13 31a 8 20 Sched. 40 in. 91a 228a 30 76a 18 46a 11 28CPVC Pipe in. 64a 159a 21 53a 13 32a 8 20 Sched. 40 in. 95a 238a 32 79a 19 48a 12 30

Note: Table based on various fixture flow rates, piping materials, and dead-end branch lengths. Calculations are based on the amount of heat required to heat the piping, the water in the piping, and the heat loss from the piping. Based on water temperature of 140F and an air temperture of 70F.a Delays longer than 30 sec are not acceptable.

Table 3(M) Approximate Time Required to Get Hot Water to a FixtureDelivery Time (sec)

Fixture Flow Rate (L/sec) 0.03 0.10 0.16 0.25

Piping Length (m) 3.1 7.6 3.1 7.6 3.1 7.6 3.1 7.6

Copper DN15 25 63a 8 21 5 13 3 8 Pipe DN22 48a 119a 16 40a 10 24 6 15Steel Pipe DN15 63a 157a 21 52a 13 31a 8 20 Sched. 40 DN20 91a 228a 30 76a 18 46a 11 28CPVC Pipe DN15 64a 159a 21 53a 13 32a 8 20 Sched. 40 DN20 95a 238a 32 79a 19 48a 12 30

Note: Table based on various fixture flow rates, piping materials, and dead-end branch lengths. Calculations are based on the amount of heat required to heat the piping, the water in the piping, and the heat loss from the piping. Based on water temperature of 60C and an air temperture of 21.1C.a Delays longer than 30 sec are not acceptable.

Table 2 Approximate Fixture and Appliance Water Flow Rates

FittingsMaximum Flow Ratesa

GPM L/SecLavatory faucet 2.0 1.3 Public non-metering 0.5 0.03 Public metering 0.25 gal/cycle 0.946 L/cycleSink faucet 2.5 0.16Shower head 2.5 0.16Bathtub faucets Single-handle 2.4 minimum 0.15 minimum Two-handle 4.0 minimum 0.25 minimum Service sink faucet 4.0 minimum 0.25 minimumLaundry tray faucet 4.0 minimum 0.25 minimumResidential dishwasher 1.87 aver 0.12 averResidential washing machine 7.5 aver 0.47 aver

a Unless otherwise noted.


Point-of-uSe HeaterSThis concept is applicable when there is a single fixture or group of fixtures that is located far from the temperature maintenance system. In such a situation, a small, instantaneous, point-of-use water heateran electric water heater, a gas water heater, or a small under-fixture stor-age type water heater of the magnitude of 6 gal (22.71 L)can be provided. (See Figure 7.) The point-of-use heater will be very cost-effective because it will save the cost of running hot water piping to a fixture that is a long distance away from the temperature maintenance system. The plumbing engineer must remember, however, that when a water heater is installed there are various code and installation requirements that must be complied with, such as those pertain-ing to T & P relief valve discharge.

Instantaneous electric heaters used in point-of-use applications can require a considerable amount of power, and may require 240 or 480 V service.

POTeNTIaL PROBLems IN CIRCULaTeD hOT WaTeR maINTeNaNCe sysTemsThe following are some of the potential prob-lems with circulated hot water maintenance systems that must be addressed by the plumb-ing designer.

Water VeloCitieS in Hot Water PiPing SyStemSFor copper piping systems, it is very important that the circulated hot water supply piping and especially the hot water return piping be sized so that the water is moving at a controlled veloc-ity. High velocities in these systems can cause pinhole leaks in the copper piping in as short a period as six months or less.

BalanCing SyStemSIt is extremely important that a circulated hot water system be balanced for its specified flows, including all the various individual loops within the circulated system. Balancing is required even though an insulated circulated line usu-ally requires very little flow to maintain satis-factory system temperatures. If the individual hot water circulated loops are not properly bal-anced, the circulated water will tend to short-circuit through the closest loops, creating high velocities in that piping system. Furthermore, the short-circuiting of the circulated hot water will result in complaints about the long delays in getting hot water at the remotest loops. If the hot water piping is copper, high velocities can create velocity erosion which will destroy the piping system.

Because of the problems inherent in manu-ally balancing hot water circulation systems, many professionals incorporate factory preset flow control devices in their hot water systems. While the initial cost of such a device is higher than the cost of a manual balancing valve, a


CONTINUINg eDUCaTION: Recirculating Domestic hot Water systems

* See text for requirements for strainers.

Fixture 1 Upfeed Hot Water System with Heater at Bottom of System.

Figure 2 Downfeed Hot Water System with Heater at Top of System.


Figure 3 Upfeed Hot Water System with Heater at Bottom of System.



preset device may be less expensive when the field labor cost for balancing the entire hot water system is included. When using a preset flow control device, however, the plumbing designer has to be far more accurate in select-ing the control devices capacity as there is no possibility of field adjustment. Therefore, if more or less hot water return flow is needed during the field installation, a new flow control device must be installed and the old one must be removed and discarded.

iSolating PortionS of Hot Water SyStemSIt is extremely important in circulated systems that shutoff valves be provided to isolate an entire circulated loop. This is done so that if individual fixtures need modification, their piping loop can be isolated from the system so the entire hot water system does not have to be shut off and drained. The location of these shutoff valves should be given considerable thought. The shutoff valves should be acces-sible at all times, so they should not be located in such places as the ceilings of locked offices or condominiums.

maintaining tHe BalanCe of Hot Water SyStemSTo ensure that a balanced hot water system remains balanced after the shutoff valves have been utilized, the hot water return system must be provided with a separate balancing valve in addition to the shutoff valve or, if the balanc-ing valve is also used as the shutoff valve, the balancing valve must have a memory stop. (See the discussion of balancing valves with memory stops below.) With a memory stop on the valve, plumbers can return a system to its balanced position after working on it rather than have the whole piping system remain unbalanced, which would result in serious problems.

ProViding CHeCk ValVeS at tHe endS of Hot Water looPSThe designer should provide a check valve on each hot water return line where it joins other hot water return lines. This is done to ensure that a plumbing fixture does not draw hot return water instead of hot supply water, which could unbalance the hot water system and cause delays in obtaining hot water at some fixtures.

a delay in oBtaining Hot Water at dead-end lineSKeep the delay in obtaining hot water at fix-tures to within the time (and branch length) parameters given previously to avoid unhappy users of the hot water system and to prevent lawsuits.

fLOW BaLaNCINg DevICesThe following are the more common types of balancing device.


Figure 4 Downfeed Hot Water System with Heater at Top of System.


Note: This piping system increases the developed length of the HW system over the upfeed systems shown in Figures 1 and 3.* See text for requirements for strainers.

Figure 5 Combination Upfeed and Downfeed Hot Water System with Heater at Bottom of System.

Note: This piping system increases the developed length of the HW system over the downfeed systems shown in Figures 2 and 4.* See text for requirements for strainers.

Figure 6 Combination Downfeed and Upfeed Hot Water System with Heater at Top of System.


fixed orifiCeS and VenturiSThese can be obtained for specific flow rates and simply inserted into the hot water return piping system. (See Figure 8.) However, extreme care should be taken to locate these devices so they can be removed and cleaned out, as they may become clogged with the debris in the water. It is recommended, therefore, that a strainer with a blowdown valve be placed ahead of each of these devices. Additionally, a strainer with a fine mesh screen can be installed on the main water line coming into the building to help prevent debris buildup in the individual strainers. Also, a shutoff valve should be installed before and after these devices so that an entire loop does not have to be drained in order to service a strainer or balancing device.

faCtory PreSet automatiC floW Control ValVeSThe same admonition about strainers and valves given for fixed orifices and venturis above applies to the installation and location of these devices. (See Figure 9.)

floW regulating ValVeSThese valves can be used to determine the flow rate by reading the pressure drop across the valve. They are available from various manufacturers. (See Figure 10.)

BalanCing ValVeS WitH memory StoPSThese valves can be adjusted to the proper setting by installing insertable pressure measuring devices (Petes Plugs, etc.) in the piping system, which indicate the flow rate in the pipe line. (See Figure 11.)

sIzINg hOT WaTeR ReTURN PIPINg sysTems aND ReCIRCULaTINg PUmPsThe method for selecting the proper size of the hot water return piping system and the recirculating pump is fairly easy, but it does require engineering judgment. First, the plumbing engineer has to design the hot water supply and hot water return piping sys-tems, keeping in mind the parameters for total developed length,1 prompt delivery of hot water to fixtures, and velocities in pipe lines. The plumbing engineer has to make assumptions about the sizes of the hot water return piping.

After the hot water supply and hot water return systems are designed, the designer should make a piping diagram of the hot water supply system and the assumed return system showing piping sizing and approximate lengths. From this piping diagram the hourly heat loss occurring in the circulated portion of the hot water supply and return systems can be determined. (See Table 4 for minimum required insulation thickness and Table 5 for approx-imate piping heat loss.)

Next determine the heat loss in the hot water storage tank if one is provided. (See Table 6 for approximate tank heat loss.) Calculate the total hot water system energy loss (tank heat loss plus piping heat loss) in British thermal units per hour (watts). This total hot water system energy loss is represented by q in Equation 1 below. Note: Heat losses from storage type water heater tanks are not nor-mally included in the hot water piping system heat loss because the water heater capacity takes care of this loss, whereas pumped hot water has to replace the piping convection losses in the piping system. (1) q = 60rwcT [q = 3600rwcT]

where 60 = min/h 3600 = sec/h q = piping heat loss, Btu/h (kJ/h) r = flow rate, gpm (L/sec) w = weight of heated water, lb/gal (kg/L) c = specific heat of water, Btu/lb/F (kJ/kg/K) T = change in heated water temperature (tem-

perature of leaving water minus temperature of incoming water, represented in this manual as Th Tc, F [K])

Therefore q = c (gpm 8.33 lb/gal)(60 min/h)(F temperature

drop) = 1(gpm) 500 F temperature drop [q = c (L/sec 1kg/L)(3600 sec/h)(K temperature drop) = 1(L/sec) 15 077 kJ/L/sec/K K temperature drop]

(2) gpm system heat loss (Btu/h)500 F temperature drop

[L/sec system heat loss (kJ/h) ]15 077 K temperature dropIn sizing hot water circulating systems, the designer should note

that the greater the temperature drop across the system, the less water is required to be pumped through the system and, therefore, the greater the savings on pumping costs. However, if the domestic hot water supply starts out at 140F (60C) with, say, a 20F (6.7C) temperature drop across the supply system, the fixtures near the end of the circulating hot water supply loop could be provided with a hot water supply of only 120F (49C). In addition, if the hot water supply delivery temperature is 120F (49C) instead of 140F (60C), the plumbing fixtures will use greater volumes of hot water to get the desired blended water temperature (see Chapter 1, Table 1.1). Therefore, the recommended hot water system temperature drop should be of the magnitude of 5F (3C). This means that if the hot water supply starts out from the water heater at a tempera-ture between 135 and 140F (58 and 60C), the lowest hot water supply temperature provided by the hot water supply system could



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Figure 7 Instantaneous Point-of-Use Water Heater Piping Diagram.Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com

be between 130 and 135F (54 and 58C). With multiple tempera-ture distribution systems, it is recommended that the recirculation system for each temperature distribution system be extended back to the water heating system separately and have its own pump.

Using Equation 2, we determine that, if there is a 5F (3C) tem-perature drop across the hot water system, the number to divide into the hot water circulating system heat loss (q) to obtain the minimum required hot water return circulation rate in gpm (L/sec) is 2500 (500 5F), (45 213 [15 071 3C]).

For a 10F (6C) temperature drop that number is 5000 (from Equation 2, 500 10F = 5000) (90 426 [from Equation 2, 15 071 6C = 90 426]). However, this 10F (6C) temperature drop may produce hot water supply temperatures that are lower than desired.

After Equation 2 is used to establish the required hot water return flow rate, in gpm (L/sec), the plumbing designer can size the hot water return piping system based on piping flow rate velocities and the available pump heads. It is quite common that a plumb-ing designer will make wrong initial assumptions about the sizes

of the hot water return lines to establish the initial heat loss figure (q). If that is the case, the plumbing engineer will have to correct the hot water return pipe sizes, redo the calculations using the new data based on the correct pipe sizing, and verify that all the rest of the calculations are now correct.

examPLe 1 CaLCULaTION TO DeTeRmINe ReQUIReD CIRCULaTION RaTe1. Assume that the hot water supply piping system has 800 ft (244 m) of average size 1 in. (DN32) pipe. From Table 5, determine the heat loss per linear foot (meter). To find the total heat loss, multiply length times heat loss per foot (meter):

800 ft 13 Btu/h/ft = 10,400 Btu/h supply piping losses(244 m 12.5 W = 3050 W supply piping losses)

2. Assume that the hot water return piping system for the system in no. 1 above has 100 ft (30.5 m) of average in. (DN15) piping and 100 ft (30.5 m) of average in. (DN20) pipe. From Table 5 determine the heat loss per linear foot (meter):

100 ft 8 Btu/h/ft = 800 Btu/h piping loss(30.5 m 7.7 W/m = 235 W piping loss)

100 ft 10 Btu/h/ft = 1000 Btu/h piping loss1800 Btu/h piping loss

(30.5 m 9.6 W/m = 293 W piping loss )528 W piping loss3. Determine the hot water storage tank heat loss. Assume the

system in no. 1 above has a 200-gal (757-L) hot water storage


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tank. From Table 6 determine the heat loss of the storage tank @ 759 Btu/h (222 W).

4. Determine the hot water systems total heat losses by totaling the various losses:

A. Hot water supply piping losses 10,400 Btu/h B. Hot water return piping losses 1,800 Btu/h C. Hot water storage tank losses 759 Btu/h Total system heat losses 12,959 Btu/h Total system piping heat losses (A + B) = 12,200 Btu/h [A. Hot water supply piping losses 3050 W B. Hot water return piping losses 527 W C. Hot water storage tank losses 222 W Total system heat losses 3799 W Total system piping heat losses (A + B) = 3577 W]

From Equation 2, using a system piping loss of 12,200 Btu/h (3577 W) and a 5F (3C) temperature drop,

12,200 Btu/h = 4.88 gpm (say 5 gpm) required hot water return circulation rate

5F temperature difference 500

3577 W = 0.29 (say 0.3) L/sec required hot water return circulation

3C temp. difference 4188.32 kJ/m3

reCalCulation of Hot Water SyStem loSSeS1. Assume that the hot water supply piping system has 800 ft

(244 m) of average size 1 in. (DN32) pipe. From Table 5 determine the heat loss per linear foot (meter):

800 ft 13 Btu/h/ft = 10,400 Btu/h piping loss(244 m 12.5 W/m = 3050 W piping loss)

2. Assume that the hot water return piping system for the system in no. 1 above has 100 ft (30.5 m) of average in. (DN15) pipe, 25 ft (7.6 m) of average in. (DN22) pipe, and

75 ft (22.9 m) of average 1 in. (DN28) pipe. From Table 5, determine the heat loss per linear foot (meter):

100 ft 8 Btu/h/ft = 800 Btu/h piping loss 25 ft 10 Btu/h/ft = 250 Btu/h piping loss 75 ft 10 Btu/h/ft = 750 Btu/h piping loss 1800 Btu/h piping loss

[30.5m7.7W/m= 235Wpipingloss



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Figure 10 Adjustable Orifice Flow Control Valve.

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Figure 11 Adjustable Balancing Valve with Memory Stop.


7.6m9.6W/m= 73Wpipingloss 22.9m9.6W/m= 220 W piping loss 528 W piping loss]

3. Determine the hot water storage tank heat loss. Assume the system in no. 1 above has a 200-gal (757-L) hot water storage tank. From Table 6 determine the heat loss of the storage tank @ 759 Btu/h (222 W).

4. Determine the systems total heat losses: A. Hot water supply losses 10,400 Btu/h B. Hot water return losses 1,800 Btu/h C. Hot water storage tank losses 759 Btu/h Total system heat losses 12,959 Btu/h Total system piping heat losses (A + B) = 12,200 Btu/h

[A. Hot water supply losses 3050 W B. Hot water return losses 528 W C. Hot water storage tank losses 222 W Total system heat losses 3800 W Total system piping heat losses (A + B) = 3578 W]

Note: The recalculation determined that the hot water system heat losses remained unchanged and that 4.88 (say 5) gpm (0.29 [say 0.3] L/sec) is the flow rate that is required to maintain the 5F (3C) temperature drop across the hot water supply system.

It should be stated that engineers use numerous rules of thumb to size hot water return systems. These rules of thumb are all based on assumptions, however, and are not recommended. It is recom-mended that the engineer perform the calculations for each project to establish the required flow rates because, with all the various capacities of the pumps available today, exact sizing is possible, and any extra circulated flow caused by the plumbing engineer using a rule of thumb equates to higher energy costs, to the detriment of the client.

esTaBLIshINg The heaD CaPaCITy Of The hOT WaTeR CIRCULaTINg PUmP

Table 4 Minimum Pipe Insulation ThicknessRequired Insulation Thickness for Piping (in.)

Runouts 2 in. or Lessa 1 in. or Less 12 in. 24 in. 5 & 6 in.

8 in. or Larger

1 1 1 1 1Note: Data based on fiberglass insulation with all-service jacket. Data will change depending on actual type of insulation used. Data apply to recirculating sections of hot water systems and the first 3 ft from the storage tank of uncirculated systems.a Uncirculated pipe branches to individual fixtures (not exceeding 12 ft in length). For lengths longer than 12 ft, use required insulation thickness shown in table.

Table 4(M) Minimum Pipe Insulation ThicknessRequired Insulation Thickness for Piping (mm)

Runouts DN32 or

LessaDN25 or

LessDN32DN50

DN65DN100

DN125 & DN150

DN200 or Larger

13 25 25 40 40 40Note: Data based on fiberglass insulation with all-service jacket. Data will change depending on actual type

of insulation used. Data apply to recirculating sections of hot water systems and the first 0.9 m from the storage tank of uncirculated systems.

a Uncirculated pipe branches to individual fixtures (not exceeding 3.7 m in length). For lengths longer than 305 mm, use required insulation thickness shown in table.

Table 5 Approximate Insulated Piping Heat Loss and Surface Temperature

Nominal Pipe Size (in.)

Insulation Thickness (in.)

Heat Loss (Btu/h/ linear ft)

Surface Temperature

(F) 1 8 68 1 10 69

1 1 10 691 1 13 701 1 13 692 or less a 24 or less 742 1 16 702 1 12 673 1 16 684 1 19 696 1 27 698 1 32 69

10 1 38 69Note: Figures based on average ambient temperature of 65F and annual average wind

speed of 7.5 mph.a Uncirculating hot water runout branches only.

Table 5(M) Approximate Insulated Piping Heat Loss and Surface Temperature

Nominal Pipe Size (mm)

Insulation Thickness (mm)

Heat Loss (W/m)

Surface Temperature

(C) DN15 25 7.7 20 DN20 25 9.6 21 DN25 25 9.6 21 DN32 25 12.5 21 DN40 25 12.5 21 DN50 or less 13a 23.1 or less 23 DN50 25 15.4 21 DN65 38 11.5 19 DN80 38 15.4 20 DN100 38 18.3 21 DN150 38 26.0 21 DN200 38 30.8 21 DN250 38 36.5 21

Note: Figures based on average ambient temperature of 18C and annual average wind speed of 12 km/h.

a Uncirculating hot water runout branches only.

Table 6 Heat Loss from Various Size Tanks with Various Insulation Thicknesses

Insulation Thickness

(in.)Tank Size

(gal)

Approx. Energy Loss from Tank at Hot Water

Temperature 140F (Btu/h)a

1 50 4681 100 7362 250 7593 500 7593 1000 1273

Source: From Sheet Metal and Air Conditioning Contractors National Association (SMACNA) Table 2 data.

a For unfired tanks, federal standards limit the loss to no more than 6.5 Btu/h/ft2 of tank surface.

Table 6(M) Heat Loss from Various Size Tanks with Various Insulation Thicknesses

Insulation Thickness

(mm)Tank Size

(L)

Approx. Energy Loss from Tank at Hot Water Temperature 60C (W)a

25.4 200 13725.4 400 21650.8 1000 22276.2 2000 22276.2 4000 373

Source: From Sheet Metal and Air Conditioning Contractors National Association (SMACNA) Table 2 data.

a For unfired tanks, federal standards limit the loss to no more than 1.9 W/m2 of tank surface.



The hot water return circulating pump is selected based on the required hot water return flow rate (in gpm [L/sec]), calculated using Equation 2, and the systems pump head. The pump head is nor-mally determined by the friction losses through only the hot water return piping loops and any losses through balancing valves. The hot water return piping friction losses usually do not include the friction losses that occur in the hot water supply piping. The reason for this is that the hot water return circulation flow is needed only to keep the hot water supply system up to the desired temperature when there is no flow in the hot water supply piping. When people use the hot water at the fixtures, there is usually sufficient flow in the hot water supply piping to keep the system hot water supply piping up to the desired temperature without help from the flow in the hot water return piping.

The only exception to the rule of ignoring the friction losses in the hot water supply piping is a situation where a hot water return pipe is connected to a relatively small hot water supply line. Relatively small here means any hot water supply line that is less than one pipe size larger than the hot water return line. The problems cre-ated by this condition are that the hot water supply line will add additional friction to the head of the hot water circulating pump, and the hot water circulating pump flow rate can deprive the last plumbing fixture on this hot water supply line from obtaining its required flow. It is recommended, therefore, that in such a situation the hot water supply line supplying each hot water return piping connection point be increased to prevent these potential problems, i.e., use in. (DN22) hot water supply piping and in. (DN15) hot water return piping, or 1 in. (DN28) hot water supply piping and in. (DN22) hot water return piping, etc.

When selecting the hot water circulating pumps head, the designer should be sure to calculate only the restrictions encoun-tered by the circulating pump. A domestic hot water system is nor-mally considered an open system (i.e., open to the atmosphere). When the hot water circulating pump is operating, however, it is assumed that the piping is a closed system. Therefore, the designer should not include static heads where none exists. For example, in Figure 1, the hot water circulating pump has to overcome only the friction in the hot water return piping not the loss of the static head pumping the water up to the fixtures because in a closed system the static head loss is offset by the static head gain in the hot water return piping.

hOT WaTeR CIRCULaTINg PUmPsMost hot water circulating pumps are of the centrifugal type and are available as either in-line units for small systems or base-mounted units for large systems. Because of the corrosiveness of hot water systems, the pumps should be bronze, bronze fitted, or stainless steel. Conventional, iron bodied pumps, which are not bronze fitted, are not recommended.

CONTROL fOR hOT WaTeR CIRCULaTINg PUmPsThere are three major methods commonly used for controlling hot water circulating pumps: manual, thermostatic (aquastat), and time clock control. Sometimes more than one of these methods are used on a system.1. A manual control runs the hot water circulating pump contin-

uously when the power is turned on. A manual control should be used only when hot water is needed all the time, 24 h a day, or during all the periods of a buildings operation. Otherwise, it is not a cost-effective means of controlling the circulating pump because it will waste energy.

Note: The method for applying the on demand concept for controlling the hot water circulating pump is a manual control.

It can be used very successfully for residential and commercial applications.2. A thermostatic aquastat is a device that is inserted into the

hot water return line. When the water in the hot water return system reaches the distribution temperature, it shuts off the circulating pump until the hot water return system tempera-ture drops by approximately 10F [5.5C]. With this method, when there is a large consumption of hot water by the plumb-ing fixtures, the circulating pump does not operate.

3. A time clock is used to turn the pump on during specific hours of operation when people are using the fixtures. The pump would not operate, for example, at night in an office building when nobody is using the fixtures.

4. Often an aquastat and a time clock are used in conjunction so that during the hours a building is not operating the time clock shuts off the circulating pump, and during the hours the building is in use the aquastat shuts off the pump when the system is up to the desired temperature.

aIR eLImINaTIONIn any hot water return circulation system it is very important that there be a means of eliminating any entrapped air from the hot water return piping. Air elimination is not required in the hot water supply piping because the discharge of water from the fixtures will eliminate any entrapped air. If air is not eliminated from the hot water return lines, however, it can prevent the proper circulation of the hot water system. It is imperative that a means of air elimi-nation be provided at all high points of a hot water return system. The plumbing engineer must always give consideration to precisely where the air elimination devices are to be located and drained. For example, they should not be located in the unheated attics of build-ings in cold climates. If the plumbing engineer does not consider the location of these devices and where they will drain, the result may be unsightly piping in a building or extra construction costs.

INsULaTIONThe use of insulation is very cost-effective. It means paying one time to save the later cost of significant energy lost by the hot water supply and return piping system. Also, insulation decreases the stresses on the piping due to thermal expansion and contraction caused by changes in water temperature. Furthermore, the proper use of insulation eliminates the possibility of someone getting burned by a hot, uninsulated water line. See Table 5 for the surface tempera-tures of insulated lines (versus 140F [60C] for bare piping).

It is recommended that all hot water supply and return piping be insulated. This recommendation exceeds some code requirements. See Table 4 for the minimum required insulation thicknesses for all systems.

If the insulated piping is installed in a location where it is sub-jected to rain or other water, the insulation must be sealed with a watertight covering that will maintain its tightness over time. Wet insulation not only does not insulate, it also releases considerable heat energy from the hot water piping, thus wasting energy. Fur-thermore, the insulation on any outdoor lines that is not sealed watertight can be plagued by birds or rodents, etc., pecking at the insulation to use it for their nests. In time, the entire hot water supply and/or return piping will have no insulation. Such bare hot water supply and/or return piping will waste considerable energy and can seriously affect the operation of the hot water system and water heaters.

The minimum required insulation thicknesses given in Table 4 are based on insulation having thermal resistivity (R) in the range of 4.0 to 4.6 ft2 h (F/Btu) in. (0.028 to 0.032 m2 [C/W] mm) on a flat surface at a mean temperature of 75F (24C). Minimum insula-




tion thickness shall be increased for materials having R values less than 4.0 ft2 h (F/Btu) in. (0.028 m2 [C/W] mm) or may be reduced for materials having R values greater than 4.6 ft2 h (F/Btu) in. (0.032 m2 [C/W] mm).1. For materials with thermal resistivity greater than 4.6

ft2 h (F/Btu) in. (0.032 m2 [C/W] mm), the minimum insulation thickness may be reduced as follows:

4.6 Table 4 thickness = New minimum thicknessActual R

( 0.032 Table 4 thickness = New minimum thickness)Actual R2. For materials with thermal resistivity less than 4.0 ft2 h (F/

Btu) in. (0.028 m2 [C/W] mm), the minimum insulation thickness shall be increased as follows:

4.0 Table 4 thickness = New minimum thickness)Actual R( 0.028 Table 4 thickness = New minimum thickness)Actual R

CONCLUsIONIn conclusion, an inappropriate hot water recirculation system can have serious repercussions for the operation of the water heater and the sizing of the water heating system. In addition, it can cause the wastage of vast amounts of energy, water, and time. Therefore, it is incumbent upon the plumbing designer to design a hot water recirculation system so that it conserves natural resources and is in accordance with the recommendations

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