High Eff HW House Boiler

Dick_3

Steve,
The original HW design temp is 175 degrees F.

Per our in-house engineer, critically sized means 240M btu/hr meets the actual heat loss on a full load day. No added capacity, but allows a diversity factor of one.

Dick_3

High Efficiency House Boiler Selection

What can you recommend as far as a high efficiency gas fired hot water boiler with 240M output?

Having 30 years of commercial/industrial HVAC experience, I'm just not familiar enough with the newer high eff "house" boilers to make a selection for a 4 tenant rental property with cast iron rad's w/ Danfoss self-powered valves.

The owner would like to reduce his fuel costs, I suggested insulating the piping in the unheated basement, an outdoor air reset controller, and a new boiler. The heat loss is critially sized at 240M. Zone control for each tenant area is out due to the common piping layout. Any other ideas?

We don't specialized in "house" work, but the owner is an industrial customer of ours looking for some help with his private investment property.

Thanks, in advance.

Chuck Shaw_4

Maybe the best choice

would be multiple condensing boilers. Two 120,000, or 3 80,000 or....well you can do the math. With the right control you could save him a nice piece of change.

Chuck

Dick_3

Good idea Chuck, multiple boilers.

What manufacturer and model would you recommend?

Chuck Shaw_4

My answer would

be biased because of who I work for. Lets wait for the others to chime in, and see what the masses say.

Chuck

Brian

Boilers

My Choice would be Buderus but in the case of multible boilers the most valuble piece of equipment is the tekmar control running them.

Good Luck
Dobber

Joe Brix

Modulating condensing boilers

would eliminate the need and expense of multiple boilers. The WM Ultra and Munchkin (or Peerless Pinnacle) could match the load.

ERIC-NJ

boiler selection

I would choose the buderus wall hung modulating boiler.They are running eff. of 97-99% EFF. and they have the outdoor reset control built in.

hr

Dual condensors

if budget allows, would be my first choice. With the proper staging control, which some manufactures offer within the onboard control, it would be the most efficient package.

When you stage multiple condensing boilers the method is a bit different than a cast boilers, for example.

When the lead boiler runs to near full capacity, the control would start to back the firing rate of the lead boiler back while starting the second boiler. By doing this you expose twice the HX surface area to ideal condensing temperatures, for highest efficiency.

Some controls will post purge residual heat after the boiler burner shuts down.

Also with dual modulating boilers you double your turndown rate. If you had one 300K input that turned down to 60K at low fire you have a 5 to 1 turndown.

With two 150K at 5 to 1 you would have a turndown from 30K (one boiler at low fire) all the way up to 300K. A 10 to 1 turndown rate! This can help a lot with multi zoned systems, under low load conditions.

Better yet with 3- 100K units for a turn down of 15 to 1 or 20K to 300K.

In some cases it would eliminate on off cycles completely. This would greatly reduce ignitor and other component cycling. Steady state firing with the output matched to the load would be ideal

hot rod

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Constantin

... or with a wider turn-down ratio of 16:1,

... the trinity 400 may be another attractive choice. It can modulate from 400kBTU to 25kBTU and hence cover not only the heating needs but can probably cover the DHW as well. However, it is but a single boiler and thus does not offer the redundancy that a dual setup may afford.

On the other hand, the Tekmar staging control had the two Buderus' in a relative's basement staging so well that they both failed from a clogged thermocouple within hours of each other (LP).

Considering that this is a apartment complex, having two Trinity 400's + a Phase III indirect may cover the heating, water, and the redundancy needs. Naturally, you'll have to make sure that the Phase III can handle the throughput requirements and that the Trinities can keep up with the demand...

Steve Ebels_3

Question for ****

What water temp is the system currently st up to run at? What do you mean by "critically sized"? No margin for error?