Water source heat pump piping

bignozzle

Just had an idea pop into my head, what if you put the ground loop piping under the basement slab when building a house. In Ct basement floors are generally 6-7’ below ground level. Thoughts?

ethicalpaul

It’s not enough area

Jamie Hall

Robbing Peter to pay Paul? Let's see. You extract heat from the ground beneath your house. You then use a heat pump to move that heat into your house. You then extract that heat from the ground beneath your house. You then...

Something wrong here.

No. Won't work.

ethicalpaul

Well extracting heat from the basement to put into the house isn’t necessarily bad…that’s what people do when they put insulation on their steam pipes

pecmsg

During heating season, that floor is going to get awful cold!

During cooling season, that floor is going to get awfully hot!

Jamie Hall

ethicalpaul said:

Well extracting heat from the basement to put into the house isn’t necessarily bad…that’s what people do when they put insulation on their steam pipes

Well... yes, but that heat to which you refer came from the boiler, not the floor of the room you are trying to heat.

WMno57

Jamie Hall said:

Robbing Peter to pay Paul? Let's see. You extract heat from the ground beneath your house. You then use a heat pump to move that heat into your house. You then extract that heat from the ground beneath your house. You then...

Agree given typical basement construction. However I firmly believe all new construction homes with basements in cold climates should have foam completely surrounding all exterior surfaces of the slab floor, walls, and wall footers. Joe Lstiburek at Building Science Corp has been a proponent of basement insulation for years.
https://buildingscience.com/
With an insulated basement and high enough water table I think it's an idea to consider. Might not provide all the heating and cooling needs, but it could contribute.

Jamie Hall

Just let me ask. Where is that heat which you are going to extract from under the slab to heat the house supposed to come from in the first place? I'll grant that if the water table is high enough, and the ground water is moving through it from one side of the house to the other, you could extract heat from that ground water (cooling it -- and the slab above it, insulation or no insulation) and dump it into the house above the slab. That would work -- the heat is being transferred by convection from the land around the house to the land under the house -- but deliberately cooling a portion of the envelope of the structure which you are trying to warm up just doesn't pass the giggle test.

f you are going to put in a shallow ground source heat pump loop system, at least put it down gradient from the structure. That way you can even recover a tiny bit of the heat you pumped into the structure in the first place.

WMno57

@Jamie Hall Thinking of two homes I have lived in.
Home 1

• 2100 sq ft ranch
  
• Full basement
  
• Standard depth basement for mid Michigan
  
• Built 1972 on what today would be designated unbuildable wetland
  
• We were in the home 45 years, the sump pit only dried out 3 or 4 times
  

Home 2

• 1 1/2 story craftsman style
  
• Large home, so large basement footprint again
  
• Built 1915 on newly drained land that was the 5300 sq mile Kankakee Marsh
  
• English basement depth (any deeper and it would have been an inground pool)
  
• All glacial outwash sand
  
• Today, all new septics required to be mound
  

100 years of drainage and ag irrigation have lowered our avg water table about 10 feet, but we still have occasional spring weather to remind us that Mother Nature is the boss.
I really don't know if it could work or not. Our government wastes all kinds of money on stupid things. How much would it cost to build a home with some instrumentation and test it?

Jamie Hall

In both of the situations you quote, @WMno57 , there was almost certainly enough ground water movement so that you would be extracting heat primarily from the moving ground water, and not -- strictly speaking -- from the ground. And as we know, moving water is a grand way to move heat around! Particularly if Mother Nature does it for you...

So in those situations, it is likely that having all or part of the heat exchange grid pipes under the house world have worked quite well. Not any better than somewhere else on the property, but not much worse, either.

ethicalpaul

@Jamie Hall I think you are highly underestimating how much heat energy is in the ground.

the amount a house takes out of it is a tiny tiny fraction

Jamie Hall

ethicalpaul said:

@Jamie Hall I think you are highly underestimating how much heat energy is in the ground.

the amount a house takes out of it is a tiny tiny fraction

I'll have to go look at my dissertation... one of the variables which had to be incorporated was the heat flux reaching the surface or the earth under glaciers...

More seriously, the heat source for ground source heat pumps -- pretty much any flavour -- is solar radiation, of which a surprising amount reaches the ground. In most areas, the ground temperature anywhere over about 20 feet down will be very close to the mean air temperature over the year, and will be -- barring someone sticking a heat pump source down there -- very stable. For a shallow grid type ground source array, I'd be happy figuring around 30 BTUh per square foot of area effectively covered by the array. The temperature of the rock increases at about 25 degrees Celsius with every kilometer of depth increase, but that varies with location. That's a good figure for most of the continental US except the Cascade ranges of the west coast and the area around Yellowstone National Park, where it is much greater.

hot_rod

A ground loop geo system is really  a solar powered system, as Jamie mentioned. The heat energy in the earth comes from the sun, not the core of the earth 

ethicalpaul

Yes, I know it comes from the sun. I never said otherwise 😃

bignozzle

Wow, really poked a hornets nest on this one!

ethicalpaul

It’s hard not to around these parts 😂

jumper

Back in the fifties a Canadian installed refrigerant piping under his backyard to heat his home with a heat pump. I believe that it took more than one season to ice up. And houses then weren't insulated or tight like now. Nowadays heat pumps are reversible so it's a matter of how much heating versus how much cooling.

If you can confidently predict your needs; then you can balance your requirements with free summer heat or free winter cold. I see architects/engineers win technology awards for incorporating far worse complications.