Impact of floor height on Ground Sourced Heat Pump performance? 1

[GHGguerilla]

To my mechanical brothers in arms:

I am looking for a reference on what the practical limitation on building height for efficient operation of a ground sourced heat pump located at the ground level.

This pertains to multi-residential buildings, and I need to know at what point that the number of stories will become the limiting factor on performance.

Help!

Sincerely,
GHGguerilla
Electrical Engineer

 

[walkes]

Huh???

Maybe you should first review some documentation on Geothermal Heat Pump systems. See

http://www.mcquay.com/McQuay/DesignSolutions/Geothermal

But the liquid loop should only be affected by pipe length not building height as you probably have a closed loop. As long as your pumps have sufficient head to pump through the system and there is not any entrained air the system should be fine. You may have some issues with building height and system static pressure which can be addressed by decoupling the system with heat exchangers in a high rise situation.

If you have distributed heat pumps they should be performing well assuming that they have sufficient flow across the compressors.

 

[GHGguerilla]

Thanks for your help walkes, your comments helped.

I was also wondering about the economic limitation. Since a taller building will require more decoupled vertical segments resulting in higher capital cost, and there will be losses in overall efficiency due to losses etc, at what point does the system become non-economic based on a Life Cycle Cost analysis?

I'm sure this is not an easy question to answer because regional effects (ie. climate) come into play.

Any suggestions though would be helpful.

 

[MintJulep]

I don't see how those factors would be any different for a conventional heat source.

I suspect that the limiting factor would be capacity. At some point the heat load will exceed the ground coil's ability to suck heat out of the earth, unless you have unlimited acerage.

 

[ChrisConley]

Generally I've found that the larger the system is the more economical it becomes when considering GSHP systems.

We've had trouble getting payback on smaller systems because the initial capital cost is relatively high. On a larger system the premium, percentage-wise, is much less and we have real dollars in savings to work with.

 

[stanlsimon]

This will be more of a question than an answer since I know very little of the load data, climate building height,etc.,etc.

The plastic pipe used for the ground loops has a pressure rating somewhere around 100psi. Each vertical 2.3 feet of building will produce 1 psi of static pressure. An additional 10psi or so is need to fill the system.

I have worked on high rise buildings that used conventional water source heat pumps. The difference with geothermal heat pumps is the lower loop temperature at winter time design conditions. (27 F) You would need to oversize the wells if decoupling the ground loop from the building loop to give additional temperature going into the heat exchanger otherwise the building loop temperature will be below the design rating of the heat pumps. There has to be a temperature drop across the heat exchanger to push the heat. The smaller the temperature difference the larger the heat exchanger.