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AC_Hacker · 01-03-11, 02:59 PM

The previous posts have all been quite helpful, but especially the previous two.

Thanks sheepdog for the programs, they are sure to become very useful tools.

I'm very interested in your mini air heat pump. Please post photos and further details of what you have done.

And thanks Fred_Fredowski, and also bigsmile for your suggestions and help.

Testing

I have been doing quite a few tests since my last post, trying to determine the optimum charge level. It has been slow going, partly because I'm logging all my data by hand. I'm currently looking to get digital pressure sensors, and also additional temperature sensors, which will make logging data automatic. It is also slow because it seems that it takes a while for a changed charge level to 'settle in'. I'm doing maybe three tests per charge level to make sure things have stabilized. I tell you, that's a lot of manual data logging.

I'm learning a good bit just about the testing procedure itself, and gradually recognizing details that will make for more repeatable tests. I've found that the ambient temperature alone plays a huge role regarding measurements general and performance data in particular. I'm also recognizing test improvements (like covering my test bucket with plastic film to stop eveporation-based heat losses) that give a more correct measure of performance variables, most importantly COP.

I do wish I had built a heat pump unit with an ATV, it would make optimization testing and adjustment much easier. In my parts bin, I have a Danfoss ATV with selectable sleeves (which cost mere than I paid for the ATV) that I will incorporate into the next unit.

Compressor Heating

But one thing I am seeing from the tests so far, which last no more than an hour, is the temperature rise in the compressor. I have noticed that varying the charge level will affect the rate of temperature rise, but in no case did it stabilize. In one test, the compressor's thermal limit switch even activated and shut of the compressor.

When I first got the de-humidifier, from which the compressor came, I ran some tests to see what its performance cycle looked like. Now I regret that I didn't assault the original unit with sensors and logged its operation to within an inch of it's life...

But it had two heat exchangers, and a fan which drew air past both of them. The front exchanger was the evaporator exchanger, and had a sensor attached not too far from where the cap tube sprayed refrigerant into the coils. The area where the sensor was placed, was the first area to frost up.

The second exchanger was behind the first and was the condenser exchanger, it received the air after it had passed through the evaporator.

So when running the de-humidifier this was the repeating cycle:

compressor-ON
frost forms on the evaporator coils
compressor-OFF
frost melts from evaporator coils and falls into the condensate bucket,
(begin again)

The cycles were spaced about seven minutes apart.

So, there are several possibilities to consider:

Perhaps this compressor was not designed to run continuously.
I still have not found the optimum charge level.
The heat exchangers I am using have excessive capacity and are forcing the compressor to do more work than it was designed for.
The cap tube needs to be re-sized to allow a larger volume of refrigerant to flow through he system to cool off the compressor.

I'd be interested in what you think...

Heat Pump Pulse Controller

I'm considering that possibly a 'pulse and glide' system may be the ultimate answer, with the heat pump adjusted to maximum COP, and tested to find the length of the running period that produces the optimum COP running period, and using that as the "pulse". Then additionally, using a very well insulated water storage tank (I've also bought 50 pounds of Calcium Chloride to use for Phase Change Material heat storage experiments) to feed the hydronic floor heating surface. (speaking of which, I have discovered that aluminum flooring is available (Alumafloor), which could be a game changer regarding lightweight hydronic floors)

I have a friend who has designed an Arduino based 'pulse controller' that will function like a very slow PCM (pulse width modulator). In it's current configuration, it will have a programmable cycle length, and a programmable pulse length, as a percentage of cycle length. I have purchased a solid state relay for the power handling. Tonight I'm going to meet up with my friend and take along the heat pump for testing.

My target configuration would be that this unit monitors heat storage tank temperature, indoor and outdoor temperature and adjusts the length of the cycle period as required.

* * * * *

By the way, I'm getting close to building my next unit. I have several compressors to choose from, and I will be ordering the heat exchangers to go with, very soon. I'll post the particulars and I invite your design input.

Best Regards,

-AC_Hacker

01-03-11, 02:59 PM	#474
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	Thanks for the posts... The previous posts have all been quite helpful, but especially the previous two. Thanks sheepdog for the programs, they are sure to become very useful tools. CoolPack can be found here. DanCap can be found here. I'm very interested in your mini air heat pump. Please post photos and further details of what you have done. And thanks Fred_Fredowski, and also bigsmile for your suggestions and help. Testing I have been doing quite a few tests since my last post, trying to determine the optimum charge level. It has been slow going, partly because I'm logging all my data by hand. I'm currently looking to get digital pressure sensors, and also additional temperature sensors, which will make logging data automatic. It is also slow because it seems that it takes a while for a changed charge level to 'settle in'. I'm doing maybe three tests per charge level to make sure things have stabilized. I tell you, that's a lot of manual data logging. I'm learning a good bit just about the testing procedure itself, and gradually recognizing details that will make for more repeatable tests. I've found that the ambient temperature alone plays a huge role regarding measurements general and performance data in particular. I'm also recognizing test improvements (like covering my test bucket with plastic film to stop eveporation-based heat losses) that give a more correct measure of performance variables, most importantly COP. I do wish I had built a heat pump unit with an ATV, it would make optimization testing and adjustment much easier. In my parts bin, I have a Danfoss ATV with selectable sleeves (which cost mere than I paid for the ATV) that I will incorporate into the next unit. Compressor Heating But one thing I am seeing from the tests so far, which last no more than an hour, is the temperature rise in the compressor. I have noticed that varying the charge level will affect the rate of temperature rise, but in no case did it stabilize. In one test, the compressor's thermal limit switch even activated and shut of the compressor. When I first got the de-humidifier, from which the compressor came, I ran some tests to see what its performance cycle looked like. Now I regret that I didn't assault the original unit with sensors and logged its operation to within an inch of it's life... But it had two heat exchangers, and a fan which drew air past both of them. The front exchanger was the evaporator exchanger, and had a sensor attached not too far from where the cap tube sprayed refrigerant into the coils. The area where the sensor was placed, was the first area to frost up. The second exchanger was behind the first and was the condenser exchanger, it received the air after it had passed through the evaporator. So when running the de-humidifier this was the repeating cycle: compressor-ON frost forms on the evaporator coils compressor-OFF frost melts from evaporator coils and falls into the condensate bucket, (begin again) The cycles were spaced about seven minutes apart. So, there are several possibilities to consider: Perhaps this compressor was not designed to run continuously. I still have not found the optimum charge level. The heat exchangers I am using have excessive capacity and are forcing the compressor to do more work than it was designed for. The cap tube needs to be re-sized to allow a larger volume of refrigerant to flow through he system to cool off the compressor. I'd be interested in what you think... Heat Pump Pulse Controller I'm considering that possibly a 'pulse and glide' system may be the ultimate answer, with the heat pump adjusted to maximum COP, and tested to find the length of the running period that produces the optimum COP running period, and using that as the "pulse". Then additionally, using a very well insulated water storage tank (I've also bought 50 pounds of Calcium Chloride to use for Phase Change Material heat storage experiments) to feed the hydronic floor heating surface. (speaking of which, I have discovered that aluminum flooring is available (Alumafloor), which could be a game changer regarding lightweight hydronic floors) I have a friend who has designed an Arduino based 'pulse controller' that will function like a very slow PCM (pulse width modulator). In it's current configuration, it will have a programmable cycle length, and a programmable pulse length, as a percentage of cycle length. I have purchased a solid state relay for the power handling. Tonight I'm going to meet up with my friend and take along the heat pump for testing. My target configuration would be that this unit monitors heat storage tank temperature, indoor and outdoor temperature and adjusts the length of the cycle period as required. * * * * * By the way, I'm getting close to building my next unit. I have several compressors to choose from, and I will be ordering the heat exchangers to go with, very soon. I'll post the particulars and I invite your design input. Best Regards, -AC_Hacker Last edited by AC_Hacker; 01-04-11 at 02:03 AM..