140 Deg. Domestic & Hot water heating system? 2

[buildingconsultants]

As part of a new condominium development, it is being suggested that we combine the domestic and hot water heating equipment into one system for a discharge temperature of 140 Deg. F. What are the cautions to design and install a system such as this?

Kind Regards,

B

 

[TBP]

I've viewed discussions between plumbing guys & heating guys (sometimes they're the one and the same) on this topic on other boards. The consensus is that there are a lot of unanwered questions regarding codes, liability and warranty issues for designers, equipment manufacturers, and installation contractors. Not the least of these are the heating loops that are out of service, but full of water, for months at a time. When these come on in the fall, they push a lot of water that has been just sitting around into the domestic loops.

If nothing else, the whole heating system will have to be designed with non-ferrous materials. The dissolved oxygen that is introduced continuously with the incoming domestic water supply will eat any iron or steel components in short order.

 

[buildingconsultants]

Thank you for you response. If we design for a building recirc. system, can we eliminate the 'dead' water that may sit for the colder seasons?

Kind Regards
B

 

[TBP]

Residential hot water heating boilers have relief valves that lift at 30 PSIG. This keeps them (and the systems they supply) out from under various ASME code requirements. This pressure won't be high enough for domestic water applications. If you use domestic water heaters, the reliefs on those lift at 150. This is great for the domestic hot water supply, but what are the ramifications for the heating system? It was also my understanding that at least some water heater manufacturers wouldn't warrant the use of their equipment for space heating applications.

I think if you move cold domestic water through the heating system in the summer to keep it circulation, you may get condensation problems. If you move hot water, you'll be heating the building when you don't need it. This will cost a lot of money to operate, and make the residents uncomfortable.

If you want the input of some people who can just run rings around me on this stuff, post your question at "

http://www.heatinghelp.com"

on the "Wall" sub-site. This is a forum for (primarily) residential/small commercial steam & hot water heating contractors and designers. My background is industrial & utility powerhouses, and these guys come at this stuff from a different angle. It's an excellent site, and I learn a lot there.

 

[buildingconsultants]

Thank you again TBP for your input, I really appreciate it!

Kind Regards
B

 

[dcasto]

I Colorado it is common to use an small hot water heater/boiler system for both domestic and heating use. There is instant hot water for the shower and you can shower all day if you wish. On the other hand, the house will get cold too.

Other thoughts: There are special temperature limiting faucets available for showers where hign temperatures are more of a safety hazard.
In a large scale operation, you'd have a Boiler operating at over 15 psig, and it would be under some local safety code any way, so that shouldn't be a problem.
Since you'll be ciculating water, you could have the water heater operate at 15 psig and then pump the heated water to 60 psig to use for heating and domestic use.
You could temper the hot water just prior to use in domestic service.

 

[cpwrocky]

Wait a minute. Are you all talking about hydronic heating? There are several systems (Apollo brand comes to mind) that have been out for many years that use a domestic hot water heater to supply both hot water for domestic use and for heating. This is very common installation, and can be very efficient. I'm in the natural gas utility industry, and we have realized for years that these are great appliances, even though the revenues we get from them are less than for heating and hot water systems separately. If I'm missing something please let me know.