The Homemade Heat Pump Manifesto

[cbearden]

Wow. So much good information from all of you!
Thanks AC, Randen, & Jeff !
I went back and put in an avg temp that we've seen in this area this year. And that definitely changes the heat load calc page.
It went from about 11000, to roughly 8200.

(7,235/8200) * 100 = 88%

If I'm looking at this correct, this could provide quite a bit of our heating needs during most of our winter months, which haven't been getting that cold. True, I may need another unit for additional supply when things do get colder. But it sounds like this could be a proof of concept that this actually works.

Randen, loved the installation pic! My wife has deemed a small 6x6 storage room where all of this will be installed in, my "command center".
This large round device at the bottom of the pic, is that your heat pump?
That looks darn impressive!
I wouldn't mind checking more details on it. Have you already posted info on here about this? I'm wondering because it looks familiar, like I've seen it before, but I can't put my finger on it.

[AC_Hacker]

Originally Posted by cbearden

I went back and put in an avg temp that we've seen in this area this year. And that definitely changes the heat load calc page.

So, you should be able to find:

• High Temp data
• Average Temp data
• Low Temp data

and also:

• Average High Temp data
• Average Low Temp data

If it were me, I'd design for the average low temp data.

But an even better bet would be to use what is known as Design Temperature. That would mean the statistically average low temp that one would expect in a typical winter in your location. This would not be the lowest temperature on record. It would also not be the lowest 3% of the coldest days. It would be a bit warmer than that, so 97% of the winter days would be warmer than the Design Temperature. If you do a little research for your area, you can find this temperature.

For Portland, my fair city, the Design Temperature is 17 degrees F.

Best,

-AC

[cbearden]

The Design temperature for my area is 20 F.
going back to my original heat load calc for my entire house,
that puts me at about 24000 btu/hr.
(7,235/24000) * 100 = 30%
I don't think this is bad for a first shot at this experiment. I'd definitely want to try to get another unit combined in with this before it's all said and done.

[AC_Hacker]

Originally Posted by cbearden

The Design temperature for my area is 20 F.
going back to my original heat load calc for my entire house,
that puts me at about 24000 btu/hr.
(7,235/24000) * 100 = 30%
I don't think this is bad for a first shot at this experiment. I'd definitely want to try to get another unit combined in with this before it's all said and done.

OK, this is very good. So now you have a well informed point from which to begin... You have a very good idea how much heat your house will lose on just about the coldest day of the year.

(NOTE: the rest of this post could go into whatever thread you choose for your loop field thread. When that thread comes available, I'll edit it into that thread.)

The paragraph below concerns the possibility of long term, trans-annual (newly-coined term) temperature decline.

The loop field ultimately gets its heat from the sun, but as I have learned, that heat can also come in the form of rain. You will withdraw heat in the winter, and heat will return in the summer. However, if your loop field is too small, so much will be withdrawn in the winter time that the summer weather will not provide full recovery to the ground where your loop field is installed. This would result in a slow, gradual lowering of the ground temperature. I have heard of cases like this already. So be mindful that your loop field is sufficiently large.


The rest of this post addresses annual heat loss & recovery...

So you you know how much HVAC derived heating capacity you will need to provide to replace that lose. As you probably know, in the HVAC world, bigger is not necessarily better. Slightly less than enough is best.

You also have the information you need, to estimate how big your loop field will need to be, in order to provide heat to your heat pump. In the case of the loop field, bigger IS better, and it is also more expensive to put in. Over the course of a winter, you'll be gradually drawing heat from your loop field, so the temperature of the loop field will be gradually declining. Along with this decline there is a small gradual reduction in efficiency of the heat pump.

If your loop field is too small, the decline of temperature would be greater and you could possibly come to a point that the water in your ground would freeze. When water freezes, there is a fairly large amount of heat that is released in the process of freezing. But after the water has frozen, the release of heat will decline because the specific heat of ice is about half the specific heat of water. Also, if the water is frozen, there will be no migration of ground water carrying more heat to to the loop field. At this point, the migration of ground heat into your loop field will be small, compared to it's pre-freeze state. Similar to the graph below:

If your loop field is over-sized, the rate of temperature decline will be lower, the rate of gradual efficiency reduction will be lower, and the likelihood of freezing the ground will be remote. However, is possible to build a loop field that is so big that the energy required to pump water through the field is no longer offset by any efficiency gains. This would be a very large loop field indeed!

The temperature of the ground in your location will be higher than it is where I live, and much higher than it is where Randen lives, in Canada. So you will need to do some local research to determine what the conventional wisdom is regarding the sizing of loop fields in your area. Specific advice that we might give you regarding the sizing of your loop field would not apply to your situation.

I would suggest calling some local GSHP outfits and asking them what is the usual size of a loop field for a 2-Ton heating load... and then go bigger.

You'll also need to find out what the soil conditions are in your area. Is the ground in your area sandy? clay? gravel? cobbles? solid rock? This will tell you whether you should do trenches or boreholes. The GSHP folks will know something about this, but the well drillers know ALL the secrets. Ask around and find someone who has drilled close to you... they are worth their weight in gold.

-AC

[cbearden]

AC,
That's good info to keep in mind. I hadn't thought about my loop field sizing affecting different variables of my system in those regards. But that makes sense as I'm reading what you posted.
There are a lot of farmers around here that's had wells put in their farms, to water them during crop seasons. Rice, most especially, and all of the mosquitoes along with it!
I'll check into some resources around here and see what I can find out about the soil/rock conditions that may be in this area.
I have dug numerous holes in our land down to about 6', and it's almost solid clay the entire way down. I'm told that there is sand deeper than that but I haven't tried digging that far down yet. We have plenty of land area to work with, so that might give me the option of putting in horizontal slinky rather than vertical.

[cbearden]

I've been looking for a used AC recovery unit so I can work on my dehumidifier for this project. I found a used microvac unit from a pawnshop seller on ebay today for about $170 shipped. But from the pics, it looks to be over 11 years old. Who knows if it works good or not still.
And then I went to a local pawnshop during lunch and found a used appion G5 twin unit for $300. It looked in good condition.
The upside to the appion is that I can ask them to power it up in the store before I buy it.
I've never priced these units before, so I wasn't sure how good/bad these might be.
suggestions?

[AC_Hacker]

Originally Posted by cbearden

I've been looking for a used AC recovery unit so I can work on my dehumidifier for this project. I found a used microvac unit from a pawnshop seller on ebay today for about $170 shipped. But from the pics, it looks to be over 11 years old. Who knows if it works good or not still.
And then I went to a local pawnshop during lunch and found a used appion G5 twin unit for $300. It looked in good condition.
The upside to the appion is that I can ask them to power it up in the store before I buy it.
I've never priced these units before, so I wasn't sure how good/bad these might be.
suggestions?

I got lucky in that I have a friend who loaned me his unit until I could find one used for $10.

You should consider whether you are likely to go into the HVAC trade, or to become an avid experimenter. While you're considering these things, you might call a local HVAC shop and ask them how much it would cost if you brought your unit in to them to extract the gas.

-AC

[cbearden]

That's a good idea...But I'd like to be able to work on these things myself, especially considering that propane may be involved later on. I already have a vacuum pump and a set of gauges, so this would compliment my tool set.
PS - awesome score on a unit for $10!

[AC_Hacker]

Originally Posted by cbearden

That's a good idea...But I'd like to be able to work on these things myself, especially considering that propane may be involved later on. I already have a vacuum pump and a set of gauges, so this would compliment my tool set.
PS - awesome score on a unit for $10!

Pretty unusual find, too.

If you poke about on the net in general and youtube in particular, you'll see that other folks have built extractor units themselves, for peanuts (real cheap). When you're extracting, you really don't have to extract past atmospheric pressure, so any HVAC compressor could be sacrificed to use in this duty.

Brad_C did some of his early work using a freezer to chill his units, and stuff for extracting. Pretty amazing, those Aussies.

You should be able to hack an extractor together pretty easily. I'm not sure what you day-job is, but if it were me, I'd try to hack one together and save my money for some really primo brazed plate heat exchangers.

* * *

By the way, you do realize that re-purposing refrigeration equipment and messing with propane can be very dangerous, right? Having a home made propane refrigeration device inside your house could cause cancellation of your insurance, at the very least... even if it was shown to not be faulty. If you proceed with this project, it is at your own risk.

-AC

[cbearden]

Aww....That's no fun! That's like telling a cat not to be curious!
I appreciate the warnings, but I'll ultimately have to weight the advantages/efficiencies against the risks.
I'd be curious to hear what others have done to mitigate these risks.
From reading other posts on this site about how R-290 is heavier and easily pools in low spots, it might be advantageous to include a couple of well-placed sensors hooked to my microcontroller as a type of an alarm.