sizing water heaters

Frank_17

I do my own sizing for installing baseboard, I have a good program. BUT.. It has nothing about water heaters, tankless or indirects. What is the correct factor or btu rating to add for both tankless and indirects?

Ken @ Amtrol

Indirect BTU load

Unless the application is commercial, additional boiler output is generally not necessary with an indirect heater. This is one of the main factors in fuel savings with this type of system. Since the indirect has a heated volume of water as a buffer, the boiler doesn't have to fire during every use. Exceptions occur when a high domestic demand is anticipated, but up-sizing a boiler will generally give you BTU's you won't use.


Ken Cerpovicz
Amtrol Inc.

Michael B

Viessmann

has a great chart showing water availability using BTU's + flow + storage. The graph is based upon their storage tanks but it gives you a good idea of how much water you can generate given all these factors. I have the chart and can fax it to you if you like..?

Terry

Think Priority

Most of the systems we design that include indirect domestic water heating do not require additional BTUs on boiler sizing IF you use priority control strategy. (Put heating demand on hold until domestic satisfied).

This can be done simply by using a relay to activate indirect pump & open contacts to primary pump on call for domestic from Aqustat. More complex systems use a Tekmar or similar control to cancel out any outdoor reset & run the boiler up to setpoint to satisfy domestic load quickly.

Hope this helps

Terry @ Frontier
heatingedm@frontier.ca

Pat

Sizing for Domestic Hot Water

George Lanthier has a great book on sizing domestic hot water.

http://www2.firedragonent.com/publications.htm

heatboy

How about...............

sizing your indirect for the bggest load? Even modest sized homes nowadays have fill and dump tubs of 80 gallons or more. I would size the indirect 25% larger than the tub. That way, depending on the indirect, you can let it recover after the tub is filled. Priority controls are OK if they are load dependent, i.e., colder the weather, shorter the priority. With newer homes having smaller heat losses per square foot and larger demands for hot water, this is something that will continue to be an issue. Either oversize the storage and size the boiler for the heat loss of the building or undersize the tank and oversize the boiler to assure recovery. There is no free lunch. If people want drive through showers and swimming pool sized tubs, it will cost 'em in the energy consumption dept.

hb

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