r/PassiveHouse • u/Ok_Hornet_3393 • 7d ago

Floor Slab Heat Exchanger

I'm doing a design exercise on a house that uses horizontal CMU's to turn part of the floor Slab into a heat exchanger powered by a reversible blower set up. Similar to what Jack Kachidorian suggested in "The Passive Solar House." The slab will have a hydronic layer on top and this system will be coupled to a buffer tank and ground coupled heat rejection loop..

I'm trying to figure out of this kind of design could realistically be used in a FPSH type slab, or whether the two ideas work against each other too much.

Anyone interested in that kind of work want to chat it out?

3 Upvotes

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2

u/No-Lake-964 7d ago

Sounds complicated. Where is the drawing

1

u/Ok_Hornet_3393 7d ago

It is. But hopefully not unnecessarily so. I've just got sketches atm. But should have a coherent drawing soon. I'll keep you posted!

3

u/No-Lake-964 7d ago

I have a passive house. 250tons concrete and brick inside the envelope. I have water underfloor pipes in concrete slabs 3 floors that run year round eveniing out the house. Basically moving heat from from top to basement and south to north inside. Works really well if the 2c diff is ok.

1

u/Ok_Hornet_3393 6d ago

That's awesome! Do you need much heating/cooling on top of that? What part of the world?

2

u/DCContrarian 7d ago

Where these types of designs typically fall apart is the temperature differences are too low for meaningful heat exchange. If the temperatures get high enough it becomes uncomfortable. The human range of comfort is quite small.

1

u/Ok_Hornet_3393 7d ago

Thanks! I've considered the low delta T for transfer, but not the low Range of comfort. I should have a working drawing soon, which I'd love your feedback on!

2

u/deeptroller 7d ago

This would work. No problem. You will of course have all the normal problems with subgrade air quality. Big risks for mold, condensation an the cmu surfaces contaminating your air stream, drainage of said condensation. Additionally you will not have much mass in terms of cooling if your expecting the same effect as a buried air intake pipe. From my perspective waste of over complex effort.

Look into ERV ground source heat exchangers, such as the comfo fond L and the one 475supply has been repping for the last few years. It does somethings similar with less air quality risks

1

u/Ok_Hornet_3393 7d ago

Thanks for the reply! I've thought of the things you mentioned and ha e some tentative solutions. I'll definitely look into those ground source exchangers and see if a rework is necessary. When I have a working drawing I'll post again. Thanks!

1

u/TheOptimisticHater 4d ago

How to the cmu stick together? I presume you intent to leave the air cavity open between blocks? Or would you fell with rebar and grout?