The Homemade Heat Pump Manifesto

[AC_Hacker]

Originally Posted by Vlad

During day time when heat demand is low and temperature outside is "high" you can gain some heat from air and transfer it to underground loop, increasing loop capacity. In my case I can add couple sun collectors on my roof, which has south exposure and during day time return line fluid before going back underground can go through sun collectors, gain heat and transfer it back to ground. At night when heat demand is high, you can extract this heat.

You are right, I hadn't counted the headers. Burying them at four feet is a very good idea...

I really like the heat reservoir idea too. Xringer has a point, if your loops are in an aquifer, the water will carry away the heat. On the other hand, if your loops are in an aquifer, the thermal transfer will be so high, and the fact that the aquifer will be refreshing the area around each loop with new warmth-bearing water, you may not need the solar boost...

However, if you decide to go with solar boost, be careful to not exceed the HDPE maximum temperature of 180 degrees. You would want at least a couple of sensors monitoring this condition, since the damage could be expensive.

It sounds like your weather and my weather are pretty much identical, with your temps being just a bit cooler.

On those freakish days when the sun come out and the sky is clear, solar collectors can really pump out some serious heat.

I have considered just such a setup with solar collectors and GSHP. It's not so unusual. The thing holding me back is that about 10 years ago, I put an aluminum shingle roof on my house, and they are not easy like composition to seal up.

I don't know what the situation is where you live, but here in the US, used flat plate solar collectors are practically being given away. In the 1970's there was a big push with government incentives, to go for solar water heat. Lots of people did it. The program was not as effective as it could have been, partly because the financial incentives were for the installation of the solar panels, not for the continued use of the panels. So after the initial pay-out from the government, there was little incentive to keep them working. Another thing is that the solar industry was very new and the "pioneers" who were the installers didn't grasp the importance of continuing customer support. The upshot is that the roofs that had the solar panels installed are now failing, and people are removing the panels and selling them very cheap, sometimes giving them away. I have ten panels in my back yard that I got for a total of $600. Because of my aluminum roof issue, I'm considering converting some of them to hydronic wall and ceiling radiators...they might even work under the floor.

Lastly, regarding the ASHP issue that you mentioned, the weather such as you and I have is actually very favorable to ASHP... The level of cold is easily within the working range of the equipment, and the heavy moisture content of the air increases the amount of available heat to be extracted, and yes it does freeze up on the coils, and there is a very effective and fast freeze sensor and defrost cycle built in (I believe the unit actually routes hot refrigerant through the frosted coils... it all happens in less than a minute). I think Xringer was indicating something about this.

[Vlad]

Unfortunately the heat you gain from condensing water (from air) is your temporary gain.
1 You will spend energy to freeze it,
2 The fan will work harder another loss
3 You will spend energy to melt it using hot gas or electric heaters
4 All time your defrost cycle is on electrical strip heater in providing heat for your furnace (with hydronic system this part can be different)

I saw heavy ice build up in just 30-40 minutes. Hot gas does melt it quick but it is not free. Residential units usually just revers the valve. Commercial units often use by-pass solenoid for defrost.

Another problem is night temperature is usually much lower then day. This makes your system even less efficient. Loop temperature is very high compare to air and stable this is why GSHP are so efficient.

My next house I will plan ahead using much more green technologies.

[NiHaoMike]

What about disconnect the heat strips so they do not operate?

[AC_Hacker]

Originally Posted by Vlad

Unfortunately the heat you gain from condensing water (from air) is your temporary gain.

Vlad,

I understand that you're a refrigeration mechanic, but I don't know if you have worked with the more recently made mini-split heat pumps.



They have evolved very rapidly and have developed many design efficiencies that, as far as I know, are not yet found on larger whole-house heat pump systems.

You might be surprised how many of the problems you mentioned, have already been solved.

I have a small (9,000 BTU) Sanyo ASHP mini-split which has about the same level of technology as the average mini-split in its class (nothing too fancy here).

It has no resistance coils at all. I am using it in a climate that is very similar to your climate. Last winter we had nearly a week when the temps went down to about 12 F. It worked just fine during this time. It used about 50% more power during that cold snap than it does on typical days, but I was quite comfortable through it all.

Yes it is true, a GSHP will be more efficient, especially so when the temperature outside goes very low.

Regards,

-AC_Hacker

[Vlad]

Originally Posted by NiHaoMike

What about disconnect the heat strips so they do not operate?

Heat strips are part of normal operating cycle of ASHP. If you disconnect them you will get cold air blown from your furnace because you are actually heating and melting the ice outside and cooling your house just like in summer . This is one of the factors that lowers efficiency of ASHP.

[Vlad]

Originally Posted by AC_Hacker

Vlad,

I understand that you're a refrigeration mechanic, but I don't know if you have worked with the more recently made mini-split heat pumps.



They have evolved very rapidly and have developed many design efficiencies that, as far as I know, are not yet found on larger whole-house heat pump systems.

You might be surprised how many of the problems you mentioned, have already been solved.

"There is no magic in the pipe"

Our instructor loved this expression. And I agree with him. You can not cheat the physical process you can improve it but you have limitations with ASHP as same as GSHP. When outside is cold your unit has to fight against big TD (air will be dry because it can not hold moisture) , sacrificing efficiency. When outside is worm your unit has to fight against freezing (the warmer the air the more moisture it will hold), again sacrificing efficiency (TD is better).
Ideal situation worm air and dry but it is not the winter scenario.

The GSHP is so efficient because it has no defrost cycle and TD is low. There is no other big factors.

[NiHaoMike]

Originally Posted by Vlad

Heat strips are part of normal operating cycle of ASHP. If you disconnect them you will get cold air blown from your furnace because you are actually heating and melting the ice outside and cooling your house just like in summer . This is one of the factors that lowers efficiency of ASHP.

Once defrost is over, the heat pump will then have to run a little longer, but it would still be more efficient than using heat strips. You can wire a relay to drop the fan speed to low so the cool air isn't as easy to notice.

There's an electromagnetic defrost heat pump that uses a burst of 915MHz, 800V AC to flash the frost into steam through dielectric heating, which then blows the rest of the frost out of the coils. That is done with a wire routed through the coils, such that it forms a transmission line with the frost as a very lossy dielectric. I don't think there are any production units but there are a few prototypes out there.

[Vlad]

Originally Posted by NiHaoMike

Once defrost is over, the heat pump will then have to run a little longer, but it would still be more efficient than using heat strips. You can wire a relay to drop the fan speed to low so the cool air isn't as easy to notice.

There's an electromagnetic defrost heat pump that uses a burst of 915MHz, 800V AC to flash the frost into steam through dielectric heating, which then blows the rest of the frost out of the coils. That is done with a wire routed through the coils, such that it forms a transmission line with the frost as a very lossy dielectric. I don't think there are any production units but there are a few prototypes out there.

In defrost cycle you STEAL heat from your house and use it for defrost. It is not magic. You cool your inside coil and heat outside. This is why you MUST let cold air flow inside your house, then you reheat it with electric heater or you will get freezing blast.

The second thing is just fantastic it will never work in real world. You just climb on roof and see what is there. You will find real environment including acids dust mice and birds crap plastic bags and more and more. You want to use 800 volt discharge you will kill somebody there may be even yourself. Many of cool inventions are only good for lab use they will never work. Over 50% of discharge lines on splits have no even insulation You know why? Because birds love it for breakfast. Another cool idea is to build huge microwave around roof top unit and use it for defrost .

Sorry if it sounds rude. It is just real life on any roof.

[NiHaoMike]

Maybe a solution is to have it store heat as hot water to use during defrost. Perhaps even have it work entirely on a hot water loop to simplify the system, although I'm not sure how much efficiency would be lost.

The high voltage would be inside the coils where it cannot be touched.

[AC_Hacker]

This is a DIY thread. The idea here is to demonstrate how to actually build a GSHP (preferably from scratch).

Perhaps 'The Billiards Room' might be a more fitting place to debate the frontiers of technology or the rumors of technology...

If someone actually has a working innovation they would like to share with the thread, that's a different matter.

Talk is cheap, action is gold.

-AC_Hacker