Ground Source Tempering Of Incoming Fresh Air.

[Ryland]

I was taking a short tour of a new house that is being built a few blocks from where I live, it's being built on a small city lot by a non profit that helps low income people and this little two bedroom house is going to be added to their low income rentals, it looks like it should be a very impressive house when it's done, PV and solar hot water on a steel roof, 4" of foam on the outside of 2x6 walls with cellulose insulation and an air to air heat exchanger, but one thing that I had not seen done before was a 300' ground loop of 1" PEX that is berried out in the yard that is going to temper the incoming air, the theory is that it will bring any incoming air up to 50F, or in the summer bring that incoming air down to 50F with a water to air heat exchanger/radiator.
I didn't get a chance to see this heat exchanger first hand because it wasn't installed yet, but assuming that the pump and fan do not draw a lot of electricity this could work really well, granted this house was around 1,000sf and super insulated but this was also only being used to temper the air, not to full on heat it or cool it, but at the same time it shouldn't take a whole lot of energy to pump water in a closed loop so doubling or tripling the size could have a decent impact on the average house and 50F incoming air is nothing to sneeze at, even more so when it's just a coil of pex and not full sized duct work that is being put underground.

[AC_Hacker]

Originally Posted by Ryland

...but one thing that I had not seen done before was a 300' ground loop of 1" PEX that is berried out in the yard that is going to temper the incoming air, the theory is that it will bring any incoming air up to 50F, or in the summer bring that incoming air down to 50F with a water to air heat exchanger/radiator...but assuming that the pump and fan do not draw a lot of electricity this could work really well, granted this house was around 1,000sf and super insulated but this was also only being used to temper the air, not to full on heat it or cool it...

I am seeing integrated units being sold by Zehnder in Europe that use the tempered air concept that you describe. They also use Heat Recovery Ventilation, heat pump water heating, heat pumps scavenging heat from inside air, after it has passed through the HRV.

Here's a photo of a combination unit from Europe that does space heating, water heating, heat recovery ventilation, and I think it also does geo-tempered air.

I tried to find a photo of an 'active' HRV, in other words, it uses a small heat pump to maximize the effect of the HRV. This is the best I could find:

At this time, these units are not being sold in the US... It would be a great hack project!

I think you edited out of your original post, some comment about how the workmen were complaining about how so much extra work was going into housing for the poor... Ha, ha, ha!!!

I think it is about time we had a little 'trickle up'!

-AC_Hacker

[strider3700]

perhaps I'm spending too much time on this board but that is a dead sexy looking system. why does all the standard crap over here have to look so bad never mind be so poorly planned out? My hot water heater never looked anything but an eyesore sitting in the middle of my basement and having a temperature gauge built in just makes sense...

[Ryland]

Originally Posted by AC_Hacker

I think you edited out of your original post, some comment about how the workmen were complaining about how so much extra work was going into housing for the poor... Ha, ha, ha!!!
-AC_Hacker

Yep, I was drifting off topic a bit, but the fact of the matter is that super insulating houses and retrofitting them like this is causing a non profit that functions off grants to see a positive cash flow, but it is sad that a few of the people who are working on it don't think it's worth while to pay attention to the details that help so much and if poor people can live in a house like this for a year or two it's going to give them some new ideals to work to, where most poor people get the hand me down junk that no one else wants.

The other thing that impresses me is that this is really being done, here in my neighbor hood! it's not being built on paper or in another country with tech that we can't find and it's not being built as a experiment that has to be tweaked and looked after every day but as a system in a house that is going to be rented to someone who is not even going to take care of it.

[AC_Hacker]

Originally Posted by Ryland

The other thing that impresses me is that this is really being done, here in my neighbor hood!

I was dead serious when I used the term 'trickle up'.

It is an incredibly interesting and powerful way to introduce eco-technology into a community.

As capitalism harnesses the compulsion toward greed, for the benefit of all (at least that was the promise), this new 'trickle up' harnesses the compulsion to be better than those that we perceive as being beneath us.

That is actually what is behind the workmen's complaint... his position in the hierarchy has been challenged.

This housing project upsets the balance in a very visible way, and creates discomfort. So it puts people who are 'better off' in a position where their only choice to restore the balance is to "Eco-Up".

Brilliant!

-AC_Hacker

[Ryland]

I got some more details about this system from the head of the project, he said that it was a 700 foot coil, not 200 foot like I was told before, they haven't picked out a pump yet so they aren't sure about electrical use either, but specs for this type of ground loop apparently say 8,000,000 BTU per year for heating or about 80 therms worth of natural gas per heating season and that it can take care of 100% of the cooling needs for the house.
This is on a house that is around 1,000 sf with two solar hot water panels for heat and just over 3kw of PV that is designed to make it a net -0- house, rented to low income people and it should make a profit.

[AC_Hacker]

Originally Posted by Ryland

I got some more details about this system from the head of the project, he said that it was a 700 foot coil, not 200 foot like I was told before, they haven't picked out a pump yet so they aren't sure about electrical use either, but specs for this type of ground loop apparently say 8,000,000 BTU per year for heating or about 80 therms worth of natural gas per heating season and that it can take care of 100% of the cooling needs for the house.
This is on a house that is around 1,000 sf with two solar hot water panels for heat and just over 3kw of PV that is designed to make it a net -0- house, rented to low income people and it should make a profit.

Well, when you see these guys again, tell them that AC_Hacker said that if they had used two 350' loops in parallel, they could have cut their circ pump power requirements by a factor of 4.

But I really love the design ideas and the very big use of insulation!

It's when this thorough heat loss minimization is carried through in such a complete fashion, then low intensity heating and cooling becomes truly workable.

And of course, the heat recovery ventilator becomes not only an important part of the design, but necessary for comfort and health.

Great stuff! Thanks for telling us about this.

-AC_Hacker

[Ryland]

Originally Posted by AC_Hacker

Well, when you see these guys again, tell them that AC_Hacker said that if they had used two 350' loops in parallel, they could have cut their circ pump power requirements by a factor of 4.
-AC_Hacker

It's that much?

We talked a bit about earth tubes as well and how people at the passive house conference are moving away from earth tubes (other then one company that has silver lined earth tubes to prevent mold growth) and that the PEX doesn't have the radon issues, rodent issues and is much more flexible.

[AC_Hacker]

Originally Posted by Ryland

It's that much?

Yeah, I'm speaking from experience on this one... The example you are citing is almost exactly the same as what I have here with my GSHP loop field.

Your example: 700 ft, one inch pipe

My loop field: 720 ft, 3/4 (.802 ID) pipe

The extra diameter in your example will certainly help out.

But factors that affect power required from a circ pump are all linear with the exception of fluid velocity in the pipe, which is the SQUARE of the velocity.

So, to get a particular required gpm, which will deliver the heat, you need a particular velocity of fluid in the pipe...

If you cut the loop length in half and run the two pipes in parallel, you have increased the effective area of the pipe by 2X, so you can reduce your fluid velocity by 1/2, which means that your friction and therefore power requirements will be reduced by a factor of 4 (since power required is directly proportional to velocity squared).

In my case, the little compressor that I am using is drawing maybe 400 watts when it runs, but the pump I was using (which was a sump pump and not an actual pump that was designed for circulation purposes) was drawing about 237 watts in operation... that is completely off the charts with regards to effficiency. I'm hoping that a real circ pump will use somewhat less power, but when I went to the engineering charts and started doing the calcs, I knew that my gains in efficiency would be pretty small. Then I looked further into the fluid mechanics involved and realized that the effective length of my pipe (which is always longer than the actual length) was pretty long for a single pump. The real surprise, the pleasant part, was when I realized that the two pipes in parallel would require half the velocity, and the aforementioned reduction in power.

The real squelcher for me was that I had all the engineering formulas in front of me before I began, but I didn't run the calcs before I did my earth work.

Bad engineer, bad engineer, bad engineer!!!

NOTE-1: 10 foot grid
NOTE-2: green circles without arrow terminations are potential sites.

I did have a niggling hunch that there might be a need to modify the single loop into two parallel branches, so I did my pipe layout in such a way that I could get to the mid-point fairly easily. (* if I had done the calculations in advance, I would not have had a niggling idea, I would have known exactly how much power I would have required from my pump to deliver the heat required from my loop field. *)

So, it is shovel time for AC_Hacker.

I will have plenty of time to contemplate on 'how much easier it is to do mathematical calculations than it is to dig a ditch'.

Best Regards,

-AC_Hacker

[Phantom]

AC_hacker are you going to be using two or one pump with the two loops? I figure if you are using two pumps depending on the demand needed it might be useful to be able to run one or both reducing the energy requirements when there is demand but demand is low.