Basic Water Heater/Boiler Design
Heat Exchanger
Casing/Cabinet
Exhaust Connection
Water In
Water Out
Air In
Air Out
Steam
Air In
Air Out
Basic Water Heater/Boiler Design
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
Basic Water Heater/Boiler Design
84%
1890–1985 1985–2001 1985–2001 2001-?
(Over Time)
Years
Fan Assisted
Combustion Air In
Air Out
Basic Water Heater/Boiler Design
Fan Assisted Combustion 1,000,000 BTU 10” vent
85%
1890–1985 1985–2001 1985–2001 2001-?
(Over Time)
Years
Fan Assisted
Combustion
Basic Water Heater/Boiler Design
99%
1890–1985 1985–2001 1985–2001 2001-?
Years
Pressurized
Combustion
Basic Water Heater/Boiler Design
Forced Draft Combustion 1,000,000 BTU 6” vent
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
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!
Adapting to maximize 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.
Adapting to maximize efficiency
§ Indirect DHW heaters - Size the heat exchanger approach temperatures as close as practical to strive for condensing compatible return water temperatures
Adapting to maximize efficiency
§ 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
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
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
(3) 50 bhp condensing Boilers replace (1) 100 bhp, remaining boilers are isolated
Efficiency upgrade - Hybrid System
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.
Efficiency upgrade - Hybrid System
§ 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
Efficiency upgrade - Hybrid System
§ 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.
Efficiency upgrade - Hybrid System
§ Shoulder season – shut down the primary boiler plant and operate on the condensing product only.
Efficiency upgrade - Hybrid System
§ 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
Efficiency upgrade - Hybrid System
§ 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
Efficiency upgrade - Hybrid System
§ 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
Efficiency upgrade - Retrofit
Low mass high efficiency boilers Dedicated fractional horsepower pumps Only on during actual burn cycle
Hydraulic Separator
Efficiency upgrade - Retrofit
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