HVAC & Plumbing Design for Multi-Family Buildings

HVAC & Plumbing Design for Multi-Family Buildings

Introduction

HVAC & Plumbing Design for Multi-Family BuildingsPresented by: Frank YarizadehDate: February 18, 2021

• Dos & Don’ts of designing HVAC & Plumbing systems for Assisted living facilities, Independent Living facilities, Apartment buildings, Hotel and Dormitories

• Q&A

Course Objectives

• Every project will encounter unique set of challenges that must be dealt with in the framework of the project specific conditions. There are no universal answers that, like a cookie cutter, satisfies all such challenges.

• The purpose of this presentation is to share some of the lessons learned in order to streamline the design process and eliminate the opportunity for any construction challenges to develop.

• Please feel free to send me your thought and valuable lessons learned so that we can update this presentation as we move forward.

Introduction

HVAC System Design

• Overview of common A/C system types: Packaged Rooftop Units: commonly used equipment consist of supply fan (single or

multiple, direct or belt drive), Direct Expansion (DX) cooling coil, compressor, with or without heat (gas or electric), and condenser. Units are available in straight cool or heat pump, constant volume (CV) or Variable Aire Volume (VAV). Chilled water units do not have compressor and condenser.

Dedicate Outside Air System: available in packaged or split system. Packaged equipment include supply fan, cooling coil, compressor, condenser and hot gas reheat coil. Equipment may include gas or electric heat and a heat recovery package.

Split system: consists of an indoor air handler coupled with an outdoor, air-cooled condensing unit. This type of system uses a direct expansion (DX) cooling coil with electric heat or is a heat pump with auxiliary electric heat.

HVAC System Design

• Overview of common A/C system types-cont’d:Water source heat pump (WSHP): a packaged unit that contains a blower, a Dx coil,

compressor, and a tube-in-tube heat exchanger. A cooling tower coupled with a flat plate heat exchanger serves as the heat sink. Single or multiple boilers are typically used as a source of heat.

Chilled water units: available in cased and uncased fan coil units concealed above ceiling, and vertical stacked units installed in a mechanical closet. Generally consist of a blower and a chilled water cooling coil. Units are available with electric and hot water heating. Units are available in 2-pipe or 4-pipe system.

Ductless split systems: similar to split systems. The indoor unit can be wall mounted, cassette ceiling type, or concealed. The wall and ceiling mounted units do not require air duct to supply and return air. Single or multiple indoor units can be coupled with a single outdoor unit.

HVAC System Design

• Overview of common A/C system- cont’d: Variable refrigerant flow/volume (VRF/VRV): similar to ductless split systems, but with

multiple indoor units connected to an outdoor unit via branch selectors. The outdoor units are available in cooling only, heat pump (system provides either heating or cooling), and heat recovery (provides heating and cooling at the same time).

Single packaged vertical air conditioners and heat pumps (VTAC/VTHP): a packaged unit that consists of a blower, cooling coil, and a condenser. Units are available as straight cool with electric heater or heat pump with auxiliary electric heat.

Packaged terminal air conditioners and heat pumps (PTAC/PTHP): similar to units described above, but are horizontal, typically installed under a window.

HVAC System Design

• General A/C system Dos & Don’ts (applies to any type of system): Do perform HVAC load calculations. Verify you output data against those in the

attached rule of thumb data (information is locate on page 46 of 791). If the two numbers are significantly different, check you input data for possible errors.

Don’t assume a sample calculation satisfies all floors and orientations. Don’t list electric heater KW at 240 volts if the power supply is 208 volts. Do coordinate location of RTUs, DOAS units, AHUs, FCUs, VTACs, and PTAC with the

architect & structural engineer. Be mind full of required service clearances and access panels.

Do indicate routing and termination of the condensate drain. For stacked units, use a condensate riser and tap at each floor with a p-trap. Drain may terminate in san. Sewer (upon approval of the AHJ) via indirect waste, dry well, storm drain (recommend installing backwater valves), or 6” above adjacent grade.

Do indicate a correctly sized return air grille or if necessary, louvered door specified by the architect.

HVAC System Design

• General A/C system Dos & Don’ts (applies to any type of system)- cont’d: To meet the outside air requirements, consider the followings:

1. Mechanical Ventilation- use DOAS equipment when approved by the owner/architect. May have to inform them about the benefits and cost associated with these equipment. a) Exception: when using CAV RTUs for the common area in hot and humid climates,

generally 10-15% outside air may be supplied by the RTU. This ratio may be increased to 20% for VAV RTUs.

2. Natural Ventilation- use operable doors and windows if the openings meet 4% of the floor area.

3. Mechanical Ventilation- as a last resort, use ducted fresh air intake subject to the following stipulations:a) Don’t oversize the intake duct.b) Provide means for balancing intake airflow.

HVAC System Design

• General A/C system Dos & Don’ts (applies to any type of system)- cont’d:c) Provide a motorized (120 VAC), normally closed damper in the intake duct and hard

wire interlock with the AHU. d) Note that the mechanical closet will get dirty because the intake air is not filtered.e) Review performance of the cooling coil based on design mixed air temperature, not

ARI conditions, to verify the supply air is at or below 55 deg. F and near saturation. Higher discharge air temp. has the potential to cause humidity issues.

4. When opting to use mechanical ventilation use of bipolar ionization devices are encouraged. These devices allow reduction of required outside air. The calculations provided by the vendor must appear on the construction drawings.

HVAC System Design

• Packaged Rooftop Units specific Dos & Don’ts: Do consider use of hot gas reheat for constant air volume (CAV) Units. This applies to

projects in the eastern half of the USA where hot and humid climate is prevalent. Do include VFDs for VAV RTUs. Do include control diagrams, points list and sequence of operations for all RTUs.

Educational training for HVAC controls coming soon. Do include Demand Control Ventilation when required by ECCC. Do include detail for installation of the roof curb and attachment of the RTU to the

curb. Do coordinate rooftop penetrations with the structural engineer. Don’t locate RTUs over noise sensitive spaces. Do schedule performance of the cooling coil based on calculated entering air DB

&WB. This will allow you to examine the leaving air DB/WB. It will be difficult to maintain 50% RH in the space when the leaving air DB exceeds 55.0 deg. F.

HVAC System Design

• Packaged Rooftop Units specific Dos & Don’ts-cont’d: Do provide 2-way or 3-way control valve for chilled water rooftop units. Do provide chilled water vestibule for chilled water units when chilled water supply

and returns are fed from below the roof.

HVAC System Design

• Split system (straight cool or heat pump) specific Dos & Don’ts: Do include a note if the air handlers require a bracket for wall mounting. Do include floor supports/stand for air handlers not supported from the closet wall. Do include means of supporting the condensing units on roof/ground. Coordinate

location of the roof mounted equipment with the architect & structural engineer.Note that equipment on the ground will require minimum 4” thick concrete pad and equipment on the roof should be installed on manufactured supports that are attached to the roof structure below.

Do provide means of securing the condensing units to the roof supports in hurricane zone area.

Do indicate routing of the refrigerant line sets. This can be covered using MME standard diagrams (details).

Do show a diagram (detail) for roof penetration of the refrigerant line sets. Do call out for the refrigerant line sets exposed on the roof to get two costs of UV

protection coating.

HVAC System Design

• Split system (straight cool or heat pump) specific Dos & Don’ts- cont’d: Don’t route refrigerant line sets through shafts with moving objects or enclosed

stairwells. Do call out for roof mounted refrigerant line sets to be supported off the roof. Do take into account that every manufacturer has a max. limit for the length of the

refrigerant line sets. Exceeding those limits effect the performance of the equipment and may cause premature compressor failure. Coordinate with the manufacturer’s rep.

Do note the performance of the air-cooled condensing units for very hot weather (parts of Arizona and California) should be based on 115 deg F, not 95 deg F.

Do avoid using heat pumps south of Orlando, Florida unless specifically requested otherwise by the owner. The economy of added cost makes for a long payback period.

HVAC System Design

• Water source heat pump specific Dos & Don’ts: Don’t over size the units in order to obtain higher efficiencies. This has cost us big $$ in

the past. Do provide a unit piping diagram that includes flow shutoff valves, strainer, manual

balancing valve or automatic flow regulator, P&T ports, and air vent. The diagram is available in MME library.

For system hydronic designs that utilize variable condenser flow, provide a two-way control valve.

Don’t specifying PVC pipe and fittings for supply and return lines, if the construction budget allows that. Have a story to tell you.

Do include floor supports/stand for WSHP units.

HVAC System Design

• Chilled water unit specific Dos & Don’ts: Do provide a coil piping diagram that includes flow shutoff valves, strainer, flow

balancing valve, 2 or 3-way flow control valve, P&T ports, and air vent. This is available in MME library.

Do avoid specifying PVC pipe and fittings for supply and return lines. Black steel, copper, or Aquatherm Blue pipe with heat fusion are preferred.

Do make sure the access panel provides access to the shutoff, flow measuring and control valves.

HVAC System Design

• Ductless split system specific Dos & Don’ts: The followings apply to applications where one outdoor unit and one or more

companion indoor unit(s) are intended to service a single alcove, one or two-bedroom residential unit.

Don’t install ceiling cassette type indoor units in a rated floor/ceiling or roof ceiling assemblies without the use of a five-sided box to house the ceiling cassette unit. Coordinate this work with the architect and the structural engineer. Note- this type of installation must be discussed with the owner/architect and the equipment manufacture to resolve spatial requirements for servicing the ceiling cassette units.

Do provide condensate pump for the indoor units.

HVAC System Design

• VRF system specific Dos & Don’ts: Reach out to mfg.'s rep to determine the best layout & arrangement in order to

maximize system performance. Mating outdoor unit(s) with indoor units that face the same orientation does not necessarily translate into an efficient operation.

Be mindful of refrigerant dispersion in occupied spaces and Refrigerant Concentration Limit (RCL). Most VRF systems use refrigerant R-410a which has an RCL 0f 0.025 lb./cubic ft. work with the followings:

1. ASHRAE Standard 15, Safety Standards for Refrigerant Systems.2. ASHRAE Standard 34, Designation and Classification of Refrigerants.3. calculate the smallest room volume in the system. Determine the amount of refrigerant in

the system including the outdoor unit, indoor units, and associated piping. Determine the refrigerant concentration.

HVAC System Design

• VRF system specific Dos & Don’ts- cont’d: Don’t install ceiling cassette type indoor units in a rated floor/ceiling or roof ceiling

assemblies without the use of a five-sided box to house the ceiling cassette unit. Coordinate this work with the architect and the structural engineer. Note- this type of installation must be discussed with the owner/architect and the equipment manufacture to resolve spatial requirements for servicing the ceiling cassette units.

Do provide condensate pump for the indoor units.

HVAC System Design

• Single Packaged Vertical Air Conditioners and Heat Pump system specific Dos & Don’ts: Do avoid First Co. & Carrier products for time being. A couple of our clients have been

experiencing issues with First Co. products and the manufacturer has been somewhat non-responsive. To the best of my knowledge, Carrier’s line of single packaged vertical A/C system is the same as First Co.

Do provide one of the two following types of access panels:1. Stamped return air grille and air filter.2. Solid access panel. Need to provide a separate wall mounted R/A Grille.

Do coordinate fancy energy management requirements with the owner/architect. These features are available at the t-stat., and are mostly applicable to hotels.

HVAC System Design

• Packaged Terminal Air Conditioners and Heat Pumps system specific Dos & Don’ts: Do coordinate the need for remote mounted t-stat with owner/architect. Do coordinate fancy energy management requirements with the owner/architect.

These features are available at the t-stat., and are mostly applicable to hotels. Do coordinate condensate drain disposal on multi-story buildings. Paint discoloration

on exterior of the building is typically an issue. Provide internal condensate drain when possible.

HVAC System Design

• Thermostats Dos & Don’ts: Do show the thermostat location on the plans. Do make sure the thermostat won’t be covered when a door is opened. Do check with the owner’s representative to determine if a specific make and

model is required. Do check the model energy code to determine if a programmable thermostat is

required. Don’t specify complicated controls as most elderly do not know how to operate

them. Don’t locate thermostats on the exterior walls. Heat conducted through exterior

walls can result in faulty reading. Don’t locate thermostats behind a TV set or any other appliance that emits heat.

This caused the thermostat to not record the space temperature accurately.

HVAC System Design

• Ductwork Dos & Don’ts: Do use sheet metal duct for bathroom exhaust, residential kitchen hood exhaust,

dryer vent, outside air intake and other general exhaust. Terminate these ducts on the exterior walls with a wall cap. On buildings with sloped roof, termination of ducts should occur in the eaves of the top floor. Note: maintain 3’ clearance between exhaust discharge and operable doors/windows and 10’ from mechanical intakes.

Unless directed otherwise by the owner/architect, consider use of fiberglass duct for the supply and return air ducts in low pressure applications up to 2” w.c.

Do use insulated flexible duct to the full extent possible. There is no length limit on flex ducts.

In buildings with rated floor/ceiling assembly, coordinate routing of the supply and return air ducts with the wood framing used for the floor trusses. Refer to the following next two slides for truss dimensions and maximum duct dimensions.

HVAC System Design

• Ductwork Dos & Don’ts- cont’d: Do show the total developed length (TDL) of the dryer vent on unit plans. Note:

1. TDL is limited to 35 feet. There is a penalty of 2.5’ for every 45-deg. and 5’ for every 90-deg. elbow.

2. If the total equivalent length exceeds 35’, request the architect to specify a dryer that allows vents longer than 35’. Must submit installation instruction to the AHJ and provide a permanent tag withing 6’ of exhaust duct connection.

3. If line items 1 and 2 don’t work, specify a dryer booster fan. This must be a last-ditch effort. Dryer booster fans add cost and require maintenance.

4. Do not specify screen at the wall caps for the dryer vents. Do show ceiling radiation dampers at ceiling mounted air distribution devices

when installed at rated floor/ceiling or roof/ceiling assemblies.1. Use either dynamic radiation damper or specify a fire stat to shutdown the air

handler.

HVAC System Design

• Ductwork Dos & Don’ts- cont’d: Do show ceiling radiation dampers at supply, return, outside air and exhaust air

duct penetrations of rated floor/ceiling or roof/ceiling assemblies. Do coordinate the need for other life safety dampers with the architectural life

safety plans. This topic was covered in a past presentation.

HVAC System Design

• Ductwork Dos & Don’ts- cont’d:

HVAC System Design

• Ductwork Dos & Don’ts- cont’d:

HVAC System Design

• Ductwork Dos & Don’ts- cont’d: Example shows a 16”x12” duct

running perpendicular to floor trusses. This and lager ducts require coordination with the structural engineer.

HVAC System Design

• Ductwork Dos & Don’ts- cont’d: Example shows how to eliminate

main supply trunks and minimize use of flex duct.

Four flex ducts connect to main supply riser above the ceiling. From there, each flex duct connects to field fabricated fiberglass plenums that in turn supplies the grilles.

Plumbing System Design

• General DWV system design Dos & Don’ts: Do specify PVC pipe and fittings to the full extent possible. Exceptions:

1. When noise is a critical issue, use Cast Ion pipe and fittings.2. Do not place PVC pipe and fittings in return air plenums unless they are wrapped with

material that meets ASTM E84. Don’t place a 3” PVC pipe in 4” framed wall. 2x4 stud walls have 3.5” of space (if

you are lucky). The OD of 3” PVC pipe is 3.5”. Don’t use makeshift DWV fittings, especially if working in AutoCAD. Refer to

plumbing code, chapter 7, for approved fittings. Do provide cleanout at the base of the stack unless a removable P-trap can be

used for that purpose. Do not offset waste stack vents between the upper and the lower fixture

connection.


• General DWV system design Dos & Don’ts- cont’d: To minimize roof penetrations, at the top floor of each residential unit, combine the

vent from washing machine stack, kitchen sink stack, and bathroom group stack below the roof line and make a single vent through the roof (VTR).

In location where there is possibility of freeze, the VTR must be 3” minimum in size. If needed, use an increaser to change a 2” vent to 3” at least one foot below the roof.

Do indicate all drainage fixture unit (DFU) calculations for the entire project and individual units.

Do coordinate invert elevations with the civil engineer. List start and end invert elevations on the construction documents.

Refer to archived presentations on the design of building drainage, waste and vent systems. They are available on the MME Academy.


• Washing Machine DWV design Dos & Don’ts: Do note that the washing machine boxes require a 2” standpipe and the

standpipe is required by code to discharge into a minimum 3” sanitary waste. Do use a separate sanitary stack for washing machines. Waste stack venting of

washing machine boxes that receive bathroom waste containing water closet discharge is prohibited by code.

Don’t place washer box in a rated wall assembly.


• Kitchen Sink DWV design Dos & Don’ts: Do use a separate waste stack to receive the discharge from kitchen sinks. Waste

stack venting of kitchen sinks that receive bathroom waste containing water closet discharge is prohibited by code.

Do provide and air admittance valve for the sink P-tap when:1. The distance from the waste stack receiving the sink waste to the sink P-trap exceeds 5’

for 1¼” waste or 6’ for 1½” waste. 2. The sink waste must be routed below the floor to connect to the waste stack.

Do call out for connection between dishwasher and kitchen sink waste. Provide an air break in the dishwasher drain.


• Bathroom Group DWV design Dos & Don’ts: Do use a wet vented system when plumbing a bathroom group consisting of a

lavatory, a tub or shower, and a water closet. Remember the wet venting rules:1. Only the fixtures in the bathroom group shall connect to the horizontal wet vent. Any

other fixture shall connect downstream of the horizontal wet vent.2. The required dry vent shall be an individual or common vent for the fixtures in the

bathroom group.3. No more than one wet vented fixture drain shall connect upstream of dry vented

fixture. 4. Size the dry vent based on the largest pipe size connected to wet vent system.5. Size the wet vent based on the table below. See next slide.

Plumbing System Design for Residential Units

6. Beware of the code requirements for maximum distance between fixture trap and vent. See table below.


• General Domestic Water system design Dos & Don’ts: Don’t use PVC pipe and fittings inside the building. This includes use of PVC pipe

and fitting in manufactured equipment such as water softeners. Do specify CPVC pipe and fittings. Inexpensive and easy to install. Be receptive to the use of Cross-Linked polyethylene (PEX) pipe. Consult with local

AHJ to determine if use of PEX pipe will be accepted. Layout options include:1. Trunk and branch2. Home-run- employs remote hot & cold water manifolds to serve fixtures3. Remote manifold- centrally located hot & cold water manifold located close to group

of fixtures.Design resources available at:https://www.huduser.gov/Publications/PDF/pex_design_guide.pdfhttps://plasticpipe.org/pdf/design-pex-plumbing-systems.pdf

https://www.huduser.gov/Publications/PDF/pex_design_guide.pdf

https://plasticpipe.org/pdf/design-pex-plumbing-systems.pdf


• General Domestic Water system design Dos & Don’ts- cont’d: Do minimize and simplify layout. See slides that follows. Don’t oversize the domestic water piping inside the units. This is especially

important when it comes to hot water pipe. The larger the pipe, the longer it takes for hot water to be dispensed. See slides that follows. ¾” HW supply is adequate for one and two-bedroom units.

Do provide mean of hot water return when using central water heating system. See slides that follows.

Do include all Domestic Water Fixture Unit (WFU) calculations for the building(s) and individual units.

Do provide means of water shutoff for each unit. Shutoff valves must be easily accessible. Don’t forget access panel if instructed to conceal shutoff valve in the wall cavity. Common location for the shutoff valves is the mechanical closet.


• General Domestic Water system design Dos & Don’ts-cont’d:

Example depicting simplification of domestic hot and cold water piping.


• General Domestic Water system design Dos & Don’ts-cont’d:

Example depicts luxury condo project where central water heating system with hot water return lines are installed. Poor location of the returns resulted in 4-5 minutes delay in hot water delivery at the remote fixtures in the condo unit.

Questions & Comments

• Questions & Comments

Questions & Comments

Documents

HVAC & Plumbing Design for Multi-Family Buildings