The Homemade Heat Pump Manifesto

[Vlad]

Originally Posted by Ko_deZ

You are missing my point. My point was not bang for the buck, it was that it will always be better with larger heat exchangers when it comes to efficiency. Yes, they get more expensive, but when you DIY, you can often get hold of some used parts cheaply or free. As long as you set up your system correctly, having larger heat exchangers will be more efficient.

This is the trap many DIY get into (including myself). The point is you have to set your goals and follow them. It is like going shopping for 2000$ car and ending up with car mortgage. You have to be reasonable. This thread attracts many people because everything discussed here is doable and doesn't need mortgage for it (and fun). I went to scarp yard another day and got monster HX from monster commercial 8 ton unit for 10$. It does make sense if you get soccer field size HX it will be more efficient. If you get it cheap or free for sure go for it but if you need to pay real $price$ then use calculator first.

As AC said it is paradox somebody who needs budget heating can't afford high efficiency system and somebody who can afford high efficiency system doesn't care to pay extra for their heating/ cooling.

[Ko_deZ]

Then Vlad, we are in agreement, larger heat sinks is always more efficient than small ones (given the right pressures). I must have misread your earlier posts.

[AC_Hacker]

Ko_deZ,

Please don't think that I have forgotten the Arduino Controller Project...

I have had a lot of unexpected issues to deal with.

It's still on my list.

-AC_Hacker

[Ko_deZ]

No problem AC, I am trying have a look here now and again in case of any questions or remarks. Hope you get all the issues dealt with.

[mrd]

Originally Posted by Vlad

As AC said it is paradox somebody who needs budget heating can't afford high efficiency system and somebody who can afford high efficiency system doesn't care to pay extra for their heating/ cooling.

It's not really a paradox; There are various ways to improve efficiency of a system, each with an up-front differential cost and a recurring savings. A cost-conscious consumer will determine how much additional funds they have available up-front for long-run savings. However, they must also weigh risks such as the possibility of not living there after X number of years.

Some alternative configurations provide better economic cost than others. If the long-run cost and up-front cost were coagulated into a single up-front cost, then you would see more rational situations where lower-income families can only afford the more efficient systems. The question then becomes is it possible to include the long-run cost into the cost of the home.

I think it is possible, for example a company could sell heat pump systems in conjunction with PV solar systems, which gives them a known up-front and long-term cost, despite fluctuations that may occur in the energy market. They can sell these installations to home builders, with a contractual obligation of the company to pay for heating/cooling costs, or all electrical costs, for X number of years, or even the life of the home. The builder can then turn around and sell the house, with the marketing bonus of no heating/electric bills to the consumer.

The question may then become how much is the builder willing to spend for such a sales advantage. It's also possible for such a contract, if it became popular, to have a known value during a real estate transaction, such that real estate agents could advise buyers how much such a contract on a potential home is worth to them.

[randen]

During the heating cycle of the larger homemade GSHP the evaporator was freezing up after about 3-4 hr run. It seems the entering water coats the inner tubes (shell & tube HX) with ice and eventually the exiting tubes into the suction side of the compressor start to frost. Not a good sign if left. Liquid refrigerant may start to enter the compressor. I had thought that the ground loop temp was getting too close to the freezing point to be effective in its pure state without anti-freeze glycol added. Ground loop temp entering 6 deg C. leaving 5 Deg C. My next test was to try the unit in aircondition mode that way the inlet temp of water would be 22 Deg. After only 1/2 hr the evaporator was freezing up. Hmm. I'm thinking antifreeze this would keep the inner surfaces clear of ice and exchange the heat. The only other thought is the evaporator isn't large enough but I cannot help but think even a larger HX would still have the same problem of freezing on the tubes on water just entering the HX.

Randen

[AC_Hacker]

Originally Posted by randen

During the heating cycle of the larger homemade GSHP the evaporator was freezing up after about 3-4 hr run. It seems the entering water coats the inner tubes (shell & tube HX) with ice and eventually the exiting tubes into the suction side of the compressor start to frost. Not a good sign if left. Liquid refrigerant may start to enter the compressor. I had thought that the ground loop temp was getting too close to the freezing point to be effective in its pure state without anti-freeze glycol added. Ground loop temp entering 6 deg C. leaving 5 Deg C. My next test was to try the unit in aircondition mode that way the inlet temp of water would be 22 Deg. After only 1/2 hr the evaporator was freezing up. Hmm. I'm thinking antifreeze this would keep the inner surfaces clear of ice and exchange the heat. The only other thought is the evaporator isn't large enough but I cannot help but think even a larger HX would still have the same problem of freezing on the tubes on water just entering the HX.

Randen

Did you ever look into this:

...then how about the ground loop flow rate through your HXs?

This would call for more pumping power. To double the flow rate in your loop, you will need 4x the pump power...

-AC

[Vlad]

Originally Posted by randen

My next test was to try the unit in aircondition mode that way the inlet temp of water would be 22 Deg. After only 1/2 hr the evaporator was freezing up. Hmm. I'm thinking antifreeze this would keep the inner surfaces clear of ice and exchange the heat. The only other thought is the evaporator isn't large enough but I cannot help but think even a larger HX would still have the same problem of freezing on the tubes on water just entering the HX.
Randen

Congratulations Randen you have just built a freezer .

I posted about this situation when you wide open water regulating valve on walk-in cooler it becomes walk-in freezer.

There is correlation between discharge temp/pressure and suction temp/pressure. The lower first the lower second. You simply over-sized your condenser.

This is downside of over-sizing condenser or evaporator. AC is right you don't have enough flow, so water starts freezing. I think it is a good idea to use antifreeze instead of water. Water will always find the way to freeze . In case of power failure circulating pump will stop circulating but refrigerant in evaporator will keep evaporating and will freeze water there.

You don't need much antifreeze just enough to keep your system happy.

[AC_Hacker]

Originally Posted by Vlad

I think it is a good idea to use antifreeze instead of water.

Keep in mind that addition of antifreeze will reduce the heat carrying capacity of your fluid and also increase the viscosity of the fluid.

There are charts that will that let you know what the reduction of heat carrying capicity is as a % of antifreeze. Ditto viscosity as a % of antifreeze.

So this all means you're gonna need a bigger loop pump. Your heat pump is extracting at a rate of nearly 2x, so you will need as a starter 4x the pump HP or watts. Then, in addition, you will need to increase pump size to compensate for heat transfer and viscosity losses.

Then there is the issue of the amount of heat your loop itself is able to supply... You could have more earth work in your future.

-AC

[randen]

AC_Hacker Wrote:

Then there is the issue of the amount of heat your loop itself is able to supply... You could have more earth work in your future.

The loop field is actually oversized and is rated at 4 Ton for this area 600 ft of 3/4 tube equals one ton and a little more than 2400 ft installed.

I'm thinking that my next step will be the antifreeze solution. Based on the comercially installed system in the house (which has the antifreeze) I'm running the same pumps used in a 6 Ton install. so the only other thing lacking is the antifreeze. The antifreeze is no small investment a 30% solution is worth about $400.00 for my loop.

Maybe the little 2 ton may have done the job. A little more refrigerant charge and antifreeze might have done it. Oh well. The joys of hacking.

Randen