The Homemade Heat Pump Manifesto

[BradC]

Originally Posted by AC_Hacker

I really appreciate your idea about brazing. It had already occured to me to do that, but the thought of how much heat it was going to take to braze the threaded pipe connections stopped me in my tracks... I was afraid I might un-braze the HX. Now that I know that it is possible to braze this up correctly, I'll give it a try.

Steel transmits heat a *lot* slower than copper or Brass. Wrap the HX in a wet (not damp, Dripping wet) cloth and heat the brass/copper mostly. The process of heating the copper/brass will transmit heat through to the steel. If you try and heat the steel to temp first you'll probably melt the brass in the process. It's a delicate balancing act. I've not brazed a PHX, but I've brazed brass fittings to steel drums.

Originally Posted by AC_Hacker

Your GSHP cooler project sounds wonderful.

I'm not doing anything new by any stretch of the imagination, but thus far I've spent about $300 in parts so I'm *way* ahead of the curve.

• Originally Posted by AC_Hacker

  What are the daily high temperatures you have there?

  The days we need the A/C are between 32 and 40 Deg C
  
  

  Originally Posted by AC_Hacker

  And what is the temperature of the water you are bringing up from your aquifer?

  Generally between 18 and 20 Deg C
  
  

  Originally Posted by AC_Hacker

  Are you also using Propane?

  Yep, the Nazis that regulate refrigerant here have the whole show so far closed it's almost impossible to get accredited to handle refrigerant without tossing in your career and doing a 4 year apprenticeship. Not a good move for a 30-something with a mortgage.
  
  

  Originally Posted by AC_Hacker

  What is the capacity of your compressor?

  I have 4 I'm playing with. The main two are as follows :
  One is a single phase ~7KW cooling capacity recip, and the other is a 3 phase ~18kw scroll. I've got a VSD for the Scroll, but I've not hooked it up yet, so most of my experiments thus far have been with the 7KW recip, or a couple of small rotaries (~14cc displacement) from window A/C's
  
  

  Originally Posted by AC_Hacker

  What type of metering device are you using?

  Right now I'm using the TEV that came with the first fan coil unit.
  
  I've just acquired 4 EEV's (three little ones ~4KW each and one ~15KW). I've just ordered some stepper driver chips and I'll build my own EEV controller to play with.
  
  

  Originally Posted by AC_Hacker

  What are the details on your heat exchangers?

  Well, somewhat agricultural to start with, I've tried ~18M of 7/8" coil in a 208L (We call them 44 Gallon, but I think they are ~55US Gallons) drum. Worked ok-ish, but after seeing what you are up to I'm looking for a PHX.
  
  

  Originally Posted by AC_Hacker

  How about your water pumps?

  Only 1 water pump as I'm using DX head units. I'm using a three phase bore pump I usually use for reticulation.
  
  

  Originally Posted by AC_Hacker

  Are you using one well for a source and the other as a sink?

  Not yet. I have one bore and I'm pulling from that at just below surface level and re-injecting back into it a couple of meters deeper. This is working for my experiments but I'm not convinced of the long term viability of this. I need to get things stable enough to do some longer term testing to watch the temps coming out of the ground.
  
  

  Originally Posted by AC_Hacker

  Are you using this system to cool the air?

  Yes. Currently I'm using the DX fan coil I got with the condensing unit, but I've just picked up a second one that I'm re-plumbing to run multi-head. Ideally I'd like to be running a chilled water loop rather than DX, but I just had a quote for over $2,000 for a couple of chilled water fan coils, whereas the last DX unit I got for $20 from the recycling station.
  
  

  Originally Posted by AC_Hacker

  How big is the air HX?

  Physically or in capacity?
  One is about 60cm x 45cm x 50cm and ~7KW total cooling, the other is about 120cm x 60cm x 45cm and *should* be good for about 14kw total cooling (far bigger than I need thus the need for the EEV)
  
  

  Originally Posted by AC_Hacker

  How many CFM are your fans?

  Both FCU's are good for about ~1000CFM.
  

Now, I "cheated" to start with. In exchange for a donation to a nominated charity, I managed to score a 7KW split system heat pump. I started by installing this and converting it to R290. I've then been plumbing various heat exchange devices in series with the air cooled condenser to experiment with lower head pressures. Out of the box the unit has a COP ~2.5, and thus far I've been able to double it by reducing the condensing temperature down to about 28 degrees.

My aim is to get the EEV's running, plumb in the second head and get the control algorithms stable. Then play with some PHX units in place of the existing condenser to try and get the condensing temperature down further. Also with the EEV's, I *should* be able to raise the evaporating temperature in response to load drops. Of course the closer the evaporating temperature to the condensing temperature, the better the COP. The other thing I need to look at is a dedicated submersible pump, preferably with speed control.

Because I inject the return bore water below the surface, the pump is effectively pumping against zero head, so it's power consumption is less than it would normally be.

Once I get that stable I'll try replacing the compressor with the scroll and see if I can improve it further by slowing the compressor as the load decreases.

Ultimately all I'm doing is taking a conventional split system heat pump and making it more efficient. I'm lucky in that I have an practically endless supply of ground water at stable temperatures.

What I did was find a scrap metal dealer than gets occasional loads of large A/C gear, and I go up and scrap it (break it down into clean as possible constituent metals) in exchange for any bits I might need. In other words, I get to spend the odd Saturday cutting A/C units apart with a 4" grinder and I can take home the bits I want.