Condensing boilers - Maximizing their value in application

Condensing boilers -Maximizing their

value in application

Jeff Deal, CEO Hamilton Engineering, Inc.

The evolution of combustion in commercial

hot water appliances in North America

First….

Basic Water Heater/Boiler Design

Heat Exchanger

Casing/Cabinet

Exhaust Connection

Water In

Water Out

Air In

Air Out

Steam

Air In

Air Out


Atmospheric fired 1,000,000 BTU 14” vent

Low Pressure – High Temperature

55-75%

1890–1985 1985–2001 1985–2001 2001-?

(Over Time)

Years

Air In

Air Out


84%

1890–1985 1985–2001 1985–2001 2001-?

(Over Time)

Years

Fan Assisted

Combustion Air In

Air Out


Fan Assisted Combustion 1,000,000 BTU 10” vent

85%

1890–1985 1985–2001 1985–2001 2001-?

(Over Time)

Years

Fan Assisted

Combustion


99%

1890–1985 1985–2001 1985–2001 2001-?

Years

Pressurized

Combustion


Forced Draft Combustion 1,000,000 BTU 6” vent

Are all condensing products created equal?

Condensing Boilers

§  Of the 35 plus brands on the market in North America, what is the product efficiency range and why is there such a variance between brands? §  99.8% to less than 90% rated maximum efficiency

and still considered condensing §  Heat exchange surface area §  Heat transfer maximization

§  Turbulent water flow §  Combustion efficiencies §  Controls

Condensing Product Efficiencies

at Low Fire

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

79 94 120 145 160

Incoming Water Temperature - °F

% E

fficie

ncy

When can products condense?

ASHRAE Handbook Chapter S27-2004 with notes

The colder the inlet water the higher the efficiency

§  Application will dictate inlet water temperatures… to a point §  Heating boilers §  Direct water heaters §  Indirect water heaters §  Pool Heaters

§  Product design and materials of construction must be compatible with the intended application

Applying condensing products in the most cost

effective way §  Retrofit or new construction design criteria

may differ in how to adapt to and if you can alter water temperatures

§  Goal number one should always be least cost of adaptations to maximize efficiency §  Doing projects in stages often makes sense to

reduce capitol costs in a given fiscal year

Adapting to maximize efficiency

§  Pool heaters - no need (80°F setpoint average), unless you go indirect, then size for 110°F - 140°F (or less) on the boiler side of the secondary heat exchanger. Remember return water temperature is the key to condensing efficiency!


§  Direct DHW heaters - An ideal application for condensing products. To maximize efficiency, consider making sure the cold incoming water enters the heater first, not the storage tank, where it will then be a blended temperature to feed the condensing appliance. §  Caution must be exercised to insure there is not

excessive restriction to flow or pressure drop as a result of having it flow through the heater first.


§  Indirect DHW heaters - Size the heat exchanger approach temperatures as close as practical to strive for condensing compatible return water temperatures


§  Heating Boilers - for space heating, consider variable water temperature (outdoor reset), during the non design outdoor temperature days. § Heating terminal type § Number of days at or below design

temperature § Room feedback reset

Retrofitting an existing high mass heating boiler

installation §  Savings will come from two fronts:

§ Condensing technology and the increase in product thermal efficiency

§  Elimination of the need to keep the boiler and boiler room piping hot 24/7and the associated stand by losses § Cycling losses during shoulder load seasons

Retrofitting an existing high mass heating boiler

installation §  Elimination of the need to keep the

boiler and boiler room piping hot 24/7and the associated standby losses

§ 100 bhp high mass firetube = 1,000 gallons of water & 10,000 lbs. of steel

§ 100 bhp of low mass condensing has less than 50 gallons of water and less than 1,000 lbs. of heat exchanger mass

Efficiency upgrade - total replacement

(1)  100 bhp Firetube hot water boiler 42.5 MBTU


(6) Condensing Boilers 6.3 MBTU ea. 37.8 MBTU total

Retrofitting an existing low mass heating boiler

installation §  High mass boilers are not the only

realistic target for upgrade §  Standard efficiency (atmospheric

combustion) tube type products §  Standby losses § Cycling losses §  Thermal efficiency upgrade



(2) Atmospheric Copper Finned Boilers 1.2 MMBTU ea.


(3) Condensing Boilers 6.3 MBTU ea.

Efficiency upgrade

§  Significant emerging trends §  The new condensing boilers can be sized for the

original calculated load plus acceptable redundancy factor §  Instead of the old single boiler equals 100% of load and

ad a second of equal capacity for redundancy (net total = 200% of design load), a two to four boiler package to equal 100% of load and one additional boiler for the redundancy factor = 120% - 150% of (new) calculated load

Efficiency upgrade

§  Significant emerging trends §  Size the new heating plant based on historical fuel

usage data and tested efficiency data from existing products §  Reductions of 35 - 80% of BTU/hr. input capacity are not

uncommon §  Takes into account all upgrades to building envelope and

heat loss calculation errors or gross ups originally done

Is total replacement required?

§  Hybrid systems allow for much better return on investment as well as flexibility in project size § Replace just a portion of the existing

equipment § Replace all of the equipment with a blend

of condensing and non-condensing products

Efficiency upgrade - Hybrid System


(2) 100 bhp and (1) 200 bhp firetube hot water boilers



(3) 50 bhp condensing Boilers replace (1) 100 bhp, remaining boilers are isolated



There will need to be of (3) motorized butterfly valves added to the system Valve 4 will be normally open and valves 2 and 3 will be normally closed. Pump 1 will be normally off.


§  The new condensing boilers can be sized for: §  Just the shoulder seasons when operating

the high mass system is most cost inefficient

§  75 - 80% of the calculated load determined by use of fuel consumption and degree day data or by calculating actual heat loss or demand loads


§  75 - 80% of the calculated load determined by use of fuel consumption and degree day data or by calculating actual heat loss or demand loads § Experience over the last 5 years has shown

that quite often, if the hybrid system is sized at 80% of anticipated maximum load, the non-condensing products will not be used at all.


§  Shoulder season – shut down the primary boiler plant and operate on the condensing product only.




§  Design differences (current, new product) between efficiency groups §  Standard efficiency - 450°F GST § Mid efficiency ~ 325°F GST § Near Condensing ~ 300°F GST § Condensing efficiency - from entering

(return) water temperature to <300°F depending on product design and return water temperature


§  Cost differences between efficiency groups

Style/designRated

EfficiencyAvg. Price 400 MBH

Avg. Price 2000 MBH

Standard efficiency 80% $4,517 $18,689Mid efficiency 84% - 85% $9,160 $22,392Near Condensing 87 - 88% $11,258 $38,990Condensing efficiency 89% - 99.8% $10,361 $45,513


§  When leaving existing product or using non-condensing product as part of the heating plant, consideration of minimum entering water temperatures to the non-condensing products

Considerations in retrofit

§  Original sizing and resulting equipment specified & installed

§  Upgrades to building envelope since boiler plant installation

§  Design water temperature, is 180 - 160°F (20°F ∆T) always or really even necessary?

Considerations in retrofit

§  Simplest and most straightforward is to reset delivered water temperature based on outdoor temperature

§  Space to be heated feedback as an upgrade to above

§  Manipulating heat distribution flow as a further upgrade

Minimizing pump horsepower

§  VFD Pumping § Delivering heat to the space with varying

building flow §  In conjunction with outdoor reset or stand alone § Considerations for required flow for “good” heat

transfer §  Terminals §  Boilers

Larger ∆T’s

§  Building re-design or new, design for higher ∆T’s to provide the ability to condense under all but the most adverse conditions

§  Designing to a 40°F or 50°F ∆T can still deliver comfort while proving cool enough returns to condense

Efficiency upgrade - Retrofit


Low mass high efficiency boilers 15:1 Turndown, dedicated fractional horsepower pumps, only on during actual burn cycle


Low mass high efficiency boilers Dedicated fractional horsepower pumps Only on during actual burn cycle

Hydraulic Separator


Low mass high efficiency boilers Dedicated fractional horsepower pumps Only on during actual burn cycle

Hydraulic Separator

Infinite flow turndown on building

Hydraulic Separators Function is to decouple flows and pressure changes between the demand side and the production side. Flow is reduced to below 0.5 fps in the separator to allow air and solids to be released from the liquid

Hydraulic Separators

§  Over 90% of the condensing products in the North American market are water tube design, so flow is critical to maintaining efficiency

§  Firetube & cast iron sectional also have minimum flows to prevent unnecessary cycling

QUESTIONS?

Condensing boilers -Maximizing their

value in application

Jeff Deal, CEO Hamilton Engineering, Inc.

Documents

Condensing boilers - Maximizing their value in application