1. Presented By: Jim Lombardo Herbert & Conway, Inc.
Hot Water Boilers
Presented By:
Jim Lombardo
Herbert & Conway, Inc.

2. Types of Hot Water Boilers
Hot water boilers are put into two general categories
Non-Condensing – Boilers with efficiencies less than 88%
Condensing Boilers – Boilers with efficiencies greater than 88%.

3. Condensing is referring to the state of the flue gas as it leaves the boiler. Has the flue gas started to condense before it leaves the boiler?

4. Types of Non-Condensing Boilers
Because the flue gases are not condensing in the boiler, the boiler heat exchanger material can be carbon steel, cast iron or copper.
Cast Iron Boilers (Peerless, Weil Mclain, Burnham). 80% Eff. Used mostly for knock down installations.
Flexible Water Tube Boilers (Cleaver Brooks FLX, Bryan RV/RW, Unilux) % Eff
Copper Fin Tube Boilers (Patterson Kelley, Lochinvar, RBI, Thermal Solutions) % Eff.
Return water temperatures must be a minimum of deg F to keep the flue gases from condensing.

5. Condensing Boilers – 88% Eff +
Condensing boilers have now become the industry standard for hot water boiler design
Boiler Efficiency is based on return water temperature and firing rate.
If the return water is below 130°F, the temperature of the flue gas can be lowered below it’s dew point and it will condense in the boiler.

6. Definition of a Condensing Boiler
A water heating device designed to recover energy normally discharged to the atmosphere through the flue.
A condensing boiler utilizes the latent heat of water produced from the burning of fuel, in addition to the standard sensible heat, to increase its efficiency.

7. When Condensing Occurs

8. Design Considerations
Efficiency
Water Volume (Thermal Mass)
Materials of Construction
Controls and Boiler Turndown
Total Installed Cost

9. Understanding Efficiency
Condensing boiler manufacturers publish efficiency curves based on return water temperature and firing rate.
Analyze the efficiency based on your operating conditions. Do not use general efficiency numbers in sales literature.

10. Efficiency vs. Return Water Temp

11. Sizing Boilers
Traditional boiler sizing is done based on peak load. Size each boiler at 2/3 peak capacity.
It is best to size one of your modular boilers based on the MINIMUM load not the maximum load in order to reduce cycling.
Rule of thumb to make sure your smallest boiler can handle the minimum load at 50% firing rate.
Make sure there is enough thermal mass in the system to reduce cycling.

12. Minimum Thermal Mass Required at Low Load
Volume = t x (Qmin Output )/[500 x Delta T]
t = Minimum desired run time in minutes – Say 10 mins
20 Degree Delta in System
1000 MBH Boiler
Volume = (10 min x 500MBH)/ (500 x 20) = 500 gallons
You cannot go wrong with more volume

13. Understanding Materials of Construction
Flue gas condensate is corrosive with a pH of Boiler heat exchanger materials of construction must accommodate the corrosive flue gas.
Most common materials for the heat exchanger are Stainless steel or cast aluminum.
Some use a combination of materials with SST in the condensing portion of the unit.
Some manufactures use materials that will corrode while condensing, but increase the metal thickness to accommodate the corrosion.

14. Thermal Conductivity of Metals
Aluminum 136 BTU/(hr-ft-degF)
Copper 231
Cast Iron
Steel
Stainless Steel 8.09

15. Controls
Non condensing boilers are more efficient at higher firing rates, so DDC system lead-lag and sequencing was easy.
Condensing boilers are more efficient at LOW fire, so to control the boilers to optimal system efficiency a new type of control scheme is needed.
Some boilers required a circulating pump on each boiler which will impact the controls and piping.

16. Remote Control Panels
Condensing boilers are staged on at low fire and remain there until all the stages have been enabled. If additional heat is required, the boilers then modulate together keeping them at the lowest firing rate possible to match the system load and maximize efficiency.
Capable of staging pumps or control valves
Remote Communication
Trending

17. On Board Controls
Many of the boiler manufactures have lead lag capability in the control that comes on the boiler.
The boiler can do basic lead lag and rotation.
One boiler is set up as the “Master” then the other boilers are wired to that boiler and are sequenced from the master. Sometimes called Mater-Member control.
Limited compared to some of the shipped loose panels but can do the basics.

18. Installed Cost vs. First Cost
Low Mass boilers typically require a circulating pump on each boiler.
Low Mass boilers may require the addition of buffer storage tanks to get the proper thermal mass in the system.
Some condensing boilers have no minimum flow requirements the therefore do not require the use if a circulating pump.
Boilers with large thermal mass may not require the buffer tank, but are larger and may require more footprint
Some smaller units can be vented with CPVC in lieu of AL294C SST.

20. Primary-Secondary

21. Variable Primary

22. Condensate Neutralization Kit Needed on Condensing Boilers
to Protect Drains from Corrosion

23. Other Opportunities for Condensing Boilers
Hybrid Systems utilizing a combination of condensing and non condensing units. Ideal for retrofits when the existing non condensing boilers are in good condition. Also possible on new projects that are price sensitive.
Hospital projects requiring standby fuel capabilities. Some manufacturers are offering #2 oil as a standby fuel for redundancy (will operate in non condensing mode when firing #2 oil).
Some manufactures offer a dual return on their boilers. This can allow a low temp loop such as domestic water or pool water to come in one connection while the building loop utilizes another connection. The boiler will condense with only a small portion of the return at low temp.
Larger Boilers now up to 12,000,000 btu/hr in a single unit.

24. Specifying Condensing Boilers
Unlike Flextube or Copper Fin Boilers which have similar construction between manufacturers, there are many different designs of condensing boilers.
All the boiler manufactures claim similar efficiencies, so how do you decide which unit is best for your application?

25. Spec Tips for Condensing Boilers
Decide on primary secondary or variable primary flow.
If variable primary, most likely choose high mass firetube design.
If primary secondary, can use high mass firetube or low mass watertube.
High mass boilers cost more but offer more flexibility because there are no (or minimal) flow restrictions. Typically regarded as more robust construction.
When listing alternate manufactures in spec, make sure it has a similar design to the basis of design.

26. Boiler Comparison – 1500 MBH
CB FLX
CB Clearfire
CFC-E
Fulton EDR
PK Sonic
AercoBMK
Thermal Solution EVCA
Water Volume
91 gal
110 gal
104 gal
23 gal
44 gal
19.8 gal
Min Flow No
Yes
Circ Pump HX
Carbon steel
SST
Copper Fin/SST combo
HX Type
Watertube
Firetube

27. Questions