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Old 11-25-12, 12:02 PM   #21
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Quote:
Originally Posted by jeff5may View Post
Adam,
If you are using this unit without a reversing valve and at temps approaching freezing, you will have to provide the evaporator coil with some form of heat to thaw it out when it freezes. It sounds like your dehumidifier control is doing its job, but without any added heat the thermistor never gets warm enough to reset the control. There are a few users experiencing this bug right now, namely hv23t and ecomodded, on their hacked heaters. If you are indeed using a dehumidifier, the evap fan runs in defrost mode while the cxr does not. In this case, you can add your choice of resistive heat element and a 120V relay with the coil wired between the fan and the cxr hot wires to sense when your unit is in defrost. The relay contacts will operate the heater element and warm the evap coil. Then when the frost has melted, the thermistor will sense the warm coil and terminate defrost. This seems like the simplest, cheapest way to accomplish defrost in your situation given the info you have provided.
The heating element will be the cheapest method but it really sucks the power to use straight electricity to defrost when there is hot gas available at a lower energy penalty.

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Old 11-25-12, 01:33 PM   #22
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My view on the subject is if it works don't fix it. If all you need is an occasional defrost, why rebuild the whole unit? With a sufficiently small heating device, it will use less power than the running cxr. Or, you could re-plumb and rewire and add controls and, and, and....have an entirely new set of problems.

Here's another wild thought that just hit me. You're heating a hot tub. Why not just throw on a mini fountain pump and flood the evap coil with your warm hot tub water? It would wire up the same way as a resistive element, maybe even without a relay. Warm hot tub water melts frost, drains into hot tub. Fifteen watt penalty. Cycle terminates by existing thermistor control, supply water drains back into hot tub. Evap fan blows away remaining water vapor, cxr starts and you're back in business.
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Old 11-25-12, 07:18 PM   #23
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The question for all makers of ASHPs is how do you best defrost for the shortest amount of time without taking heat from the conditioned space. Most older traditional HPs would have a relay that would turn on every 30-60 minutes for a set period of time and/or measure the suction temp which should be well above freezing. With forced air HPs, the interior air often got too cold as the heat from indoors was used to defrost the coil, so finding ways to minimize it is important. At least with water heating there is a large source of heat and with a reversing valve, the heat comes from tank which was produced at a good COP. What you do depends on your goal.....if you will be defrosting every 1/2 hour, 5min of straight electricity is a lot of power, 2 steps forward and 1 back.

What is a cxr? I haven't seen that term.
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Old 11-25-12, 10:17 PM   #24
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Quote:
Originally Posted by Mikesolar View Post
The question for all makers of ASHPs is how do you best defrost for the shortest amount of time without taking heat from the conditioned space.

Adam said he is using a control board from a dehumidifier.

At least with water heating there is a large source of heat and with a reversing valve, the heat comes from tank which was produced at a good COP.

This is why I had the wild idea. With a novel, cheap, reliable magdrive/jebo/eco pump, he can use his warm hot tub as a heat source for defrost.

What you do depends on your goal.....if you will be defrosting every 1/2 hour, 5min of straight electricity is a lot of power, 2 steps forward and 1 back.

With my ASHP window shaker beast machines, I went both ways, both cheap as dirt and utterly reliable.
With the first unit, I simply chopped the lines at the top of the cxr. I got lucky with that one, because the thermostat had two control output terminals. I simply moved the cxr from the "cool" to the "heat" output connector. I plan on adding a defrost klixon to that one so it stops running when the suction line gets to around 20 degrees f. Then, when and if the line warms to above 40, the unit will start up again.

The second unit is a different story. It had been modified by a previous "pro" when the original compressor died. It's still being debugged as we speak, since Murphy's Law is still being beaten out of the unit. The main issue with the unit is leaks from adding a reversing valve to the refrigerant circuit. On a positive note, the defrost control I purchased on ebay for under 5 dollars works like magic. It's an ICM 315.


What is a cxr? I haven't seen that term.
CXR is short for chest xray seriously, cxr is short for compressor.

To help others reading this thread, I will share my learnings about defrost control boards. There are only a few OEM suppliers of these boards, ICM, ICP, and Ranco being the three largest. From these few manufacturers come hundreds if not thousands of rebranded control boards.

The simplest type of board is the ICM 300 type, aka 621 dash whatever, aka Ranco DT-1. They use a separate defrost relay. They get power from a defrost klixon thermostat, which clicks on at a set temperature corresponding to a frozen evaporator. The board delays defrost a set amount of time before initiating defrost via the relay. When the evap coil warms up enough to click off the defrost thermostat, the control board loses power, the relay is deenergized and the unit goes back to normal operation. If the defrost klixon isn't satisfied, the control board ends defrost after ten minutes. It starts timing again, and defrosts after time runs out again.

The type I bought has its defrost relay on the board. It also can be wired to run off a klixon thermostat, but it doesn't have to. It has a thermistor which does the same job without any moving parts. This one, an ICM 315, is the same as a Ranco E-15 or an Avion DFT-100. It isn't quite as universal as the above board, since it has only one set of relay contacts and a standard defrost relay has three. Otherwise, it works basically the same: preset delay time, check thermistor sensor, defrost if too cold. When thermistor senses warmth, end defrost and start timing again.

There are maybe a dozen basic variations on these two designs, tailored to fit more elaborate units. HVAC techs stock a few each of their preferred brand of boards in their truck and are covered for 99.9 percent of every unit they will encounter in the field. For the other 0.1 percent, one of the stock boards will drop in with a little sorcery or the customer can pay 500 dollars for the (rebranded) 15 digit number (same) board.

My opinion is this: if you want to make your own temperature controller defrost microcomputer, go right ahead. It can be expanded later to stream real-time chest x-rays of your unit to your iphone if you want it to. But the pros go with what works and what is common. When mother nature wreaks havoc on the world, that 5 dollar timer will probably survive. If not, tech comes and swaps board in 10 minutes for 250 dollars to get you going today. Or you can do it yourself for 5 dollars. Or you can spend countless hours trying to figure out why your microcontroller went insane.
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Old 11-25-12, 11:19 PM   #25
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Mike wrote:
"With forced air HPs, the interior air often got too cold as the heat from indoors was used to defrost the coil, so finding ways to minimize it is important."

The Sanyos (and other mini-splits) do a pretty good job of defrosting the outdoor coil,
by switching the refrigerant flow, but not using the indoor fan.
At least not that can be noticed. It might be running at 10 RPMs.. Can't hear it.
But if you put your hand under the indoor unit, you can feel a slow flow of very cold air.
Scanning the coil shows it can be down around 30F. Chills the area under the unit a little.
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Old 11-26-12, 03:30 AM   #26
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Wow, thanks for the flood of input everyone! Didn't expect so much response to that post. Jeff5may, it sounds like my dehu defrost is very similar to what most central heat pumps run, with the possible exception of the timer to kick it out of defrost if the thermistor isn't satisfied. Still going to have to run some further testing to determine if that is indeed the case. I got cold and went inside for about 10 minutes and there is a slight chance the compressor cycled on and back off in that time with the way I had it set up, and I just missed it.

Little history, last year I had this thing running and heating my hottub succesffully, but frosting was a continual problem. Here's the thread that details my journey: http://ecorenovator.org/forum/geothe...ater-hp-5.html

This year instead of just having the condenser dipped in the tub, which was inefficient, ugly, and somewhat dangerous, I've built a tube-in-tube type heat exchanger around the current condensing coil. I finished stripping the fins off, cut the metal brackets off(very painstaking process not to nick a tube) and over winter break will encase them in PVC pipes. I know it seems like a lot of work to avoid simply opening up the system, but for not i REALLY DON'T want to open it up. I don't have the equipment or know-how to take that step and am not ready to make the investment at this point, and a tube in tube should be pretty efficient as-is. There's over 30 ft of tubing from that coil.

You all will be happy to know I finally invested in a Kill-A-Watt as suggested in my other thread, so I can get accurate power draw readings.

Last year in below freezing weather, when I'd get frost, I'd simply turn off the unit totally for a few minutes and it would melt the frost, but usually not completely. I attribute it to heat in the refrigerant migrating to the evap. To control this I tried a simple Klixon thermostat from another air conditioner, with the sensing bulb on the suction line of the compressor. Problem was that spot would warm up quickly enough after the compressor shut off that it never defrosted much. My hope is the heat from the compressor will be enough to bring my dehu board out of defrost, and its timer system will keep the compressor off long enough to allow the coil to melt and dry. If not, Fischertechnik microcontroller here I come.

Below freezing temps will probably still be a problem with melting the frost and last night I was thinking of manual ways to defrost it. I had the idea of soaking the coil with hottub water, but I don't think it would dry, leaving me with a block of ice when the comp restarted. Resistance would be easy, but with my small evap, I may be defrosting often enough that it would seriously impact my total COP numbers. Another option I got from research is a second coil, or some tubing in front of the evap I could pump hot water from the hottub through with the fan running. It would warm the air and melt the coil quickly and aid in drying it. I already own the small mag-drive fountain pump I would use, and a coil, from the same dehu the board I'm using came from. I think I just found my solution. The relay setup for this shouldn't be too complicated either. Some dehu's accomplish this by simply reversing the fan direction so the air passes over the condensing coil then evap, with the compressor still running. The heat is enough to bring the evap above freezing. I would turn off my compressor to speed the process up.

I wish they made window heat pumps for the US market. I've seen them in many Youtube videos in other countries(like Australia) where they have 220v mains, but never 110v versions. That would make my job ALOT simpler right now. A hot gas bypass or reversing valve system would be a god-send, and at some point I will do that if I ever open up this system. I'll also double(at least) the size of the evap to increase efficiency, and build a proper ref-water hx for the condenser side. I'll also probably add a ref-liquid(glycol) HX on the evap side to take advantage of the solar water panels I have, but that's another story.

Only 26 days until winter break and I can get back to work on this project!

Adam
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Old 11-26-12, 06:32 AM   #27
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Quote:
Originally Posted by jeff5may View Post
CXR is short for chest xray seriously, cxr is short for compressor.

To help others reading this thread, I will share my learnings about defrost control boards. There are only a few OEM suppliers of these boards, ICM, ICP, and Ranco being the three largest. From these few manufacturers come hundreds if not thousands of rebranded control boards.

The simplest type of board is the ICM 300 type, aka 621 dash whatever, aka Ranco DT-1. They use a separate defrost relay. They get power from a defrost klixon thermostat, which clicks on at a set temperature corresponding to a frozen evaporator. The board delays defrost a set amount of time before initiating defrost via the relay. When the evap coil warms up enough to click off the defrost thermostat, the control board loses power, the relay is deenergized and the unit goes back to normal operation. If the defrost klixon isn't satisfied, the control board ends defrost after ten minutes. It starts timing again, and defrosts after time runs out again.

The type I bought has its defrost relay on the board. It also can be wired to run off a klixon thermostat, but it doesn't have to. It has a thermistor which does the same job without any moving parts. This one, an ICM 315, is the same as a Ranco E-15 or an Avion DFT-100. It isn't quite as universal as the above board, since it has only one set of relay contacts and a standard defrost relay has three. Otherwise, it works basically the same: preset delay time, check thermistor sensor, defrost if too cold. When thermistor senses warmth, end defrost and start timing again.

There are maybe a dozen basic variations on these two designs, tailored to fit more elaborate units. HVAC techs stock a few each of their preferred brand of boards in their truck and are covered for 99.9 percent of every unit they will encounter in the field. For the other 0.1 percent, one of the stock boards will drop in with a little sorcery or the customer can pay 500 dollars for the (rebranded) 15 digit number (same) board.

My opinion is this: if you want to make your own temperature controller defrost microcomputer, go right ahead. It can be expanded later to stream real-time chest x-rays of your unit to your iphone if you want it to. But the pros go with what works and what is common. When mother nature wreaks havoc on the world, that 5 dollar timer will probably survive. If not, tech comes and swaps board in 10 minutes for 250 dollars to get you going today. Or you can do it yourself for 5 dollars. Or you can spend countless hours trying to figure out why your microcontroller went insane.
I've used the Ranco before and done many things to adapt defrost mechanisms to different machines and it is still a pain IF the goal is the lowest cost overall heating (best COP). One problem with trying to adapt an existing defrost control is that they are usually have some embedded safeties, for example, I tried to adapt an 18 seer York heat pump to have a liquid condenser but it was a 2 stage cxr (I should have been more awake when i asked that question) but got no joy because the control would only recognize signals from defrost or indoor that it expected. Anything else and it would lock out.

This is why we are designing our own controller where we can change the PID to suit the situation and control pumps etc.

Back to the point......I like the idea of small pump as you have suggested. It really depends on how that water can be dumped on the coil in a logical manner.
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Old 11-26-12, 06:35 AM   #28
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Wow, thanks for the flood of input everyone! Didn't expect so much response to that post. Jeff5may, it sounds like my dehu defrost is very similar to what most central heat pumps run, with the possible exception of the timer to kick it out of defrost if the thermistor isn't satisfied. Still going to have to run some further testing to determine if that is indeed the case. I got cold and went inside for about 10 minutes and there is a slight chance the compressor cycled on and back off in that time with the way I had it set up, and I just missed it.

Little history, last year I had this thing running and heating my hottub succesffully, but frosting was a continual problem. Here's the thread that details my journey: http://ecorenovator.org/forum/geothe...ater-hp-5.html

This year instead of just having the condenser dipped in the tub, which was inefficient, ugly, and somewhat dangerous, I've built a tube-in-tube type heat exchanger around the current condensing coil. I finished stripping the fins off, cut the metal brackets off(very painstaking process not to nick a tube) and over winter break will encase them in PVC pipes. I know it seems like a lot of work to avoid simply opening up the system, but for not i REALLY DON'T want to open it up. I don't have the equipment or know-how to take that step and am not ready to make the investment at this point, and a tube in tube should be pretty efficient as-is. There's over 30 ft of tubing from that coil.

You all will be happy to know I finally invested in a Kill-A-Watt as suggested in my other thread, so I can get accurate power draw readings.

Last year in below freezing weather, when I'd get frost, I'd simply turn off the unit totally for a few minutes and it would melt the frost, but usually not completely. I attribute it to heat in the refrigerant migrating to the evap. To control this I tried a simple Klixon thermostat from another air conditioner, with the sensing bulb on the suction line of the compressor. Problem was that spot would warm up quickly enough after the compressor shut off that it never defrosted much. My hope is the heat from the compressor will be enough to bring my dehu board out of defrost, and its timer system will keep the compressor off long enough to allow the coil to melt and dry. If not, Fischertechnik microcontroller here I come.

Below freezing temps will probably still be a problem with melting the frost and last night I was thinking of manual ways to defrost it. I had the idea of soaking the coil with hottub water, but I don't think it would dry, leaving me with a block of ice when the comp restarted. Resistance would be easy, but with my small evap, I may be defrosting often enough that it would seriously impact my total COP numbers. Another option I got from research is a second coil, or some tubing in front of the evap I could pump hot water from the hottub through with the fan running. It would warm the air and melt the coil quickly and aid in drying it. I already own the small mag-drive fountain pump I would use, and a coil, from the same dehu the board I'm using came from. I think I just found my solution. The relay setup for this shouldn't be too complicated either. Some dehu's accomplish this by simply reversing the fan direction so the air passes over the condensing coil then evap, with the compressor still running. The heat is enough to bring the evap above freezing. I would turn off my compressor to speed the process up.

I wish they made window heat pumps for the US market. I've seen them in many Youtube videos in other countries(like Australia) where they have 220v mains, but never 110v versions. That would make my job ALOT simpler right now. A hot gas bypass or reversing valve system would be a god-send, and at some point I will do that if I ever open up this system. I'll also double(at least) the size of the evap to increase efficiency, and build a proper ref-water hx for the condenser side. I'll also probably add a ref-liquid(glycol) HX on the evap side to take advantage of the solar water panels I have, but that's another story.

Only 26 days until winter break and I can get back to work on this project!

Adam
If you are stripping the aluminum off the coil, I hope you counted the fins and approximate surface area because somehow you will have to make up surface area in another way, perhaps a liquid jacket around some of the tubing. Anything you can leave on the pipe will help in heat transfer.
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Old 11-26-12, 08:08 PM   #29
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Mike, I'm only taking the fins off the condenser side, which will then be in water in a tube in shell type design HX. The fact that the condensing tubes are encased in larger tubes with water flowing over them should more than make up for the fact that theres not fins.

Adam
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Old 12-16-12, 01:09 AM   #30
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We've finally had a few nights where the temperature has fallen to a level where the unit has frosted up - and the defrost works perfectly.

I did make a couple of small changes to the temperature that it operates at and to the defrost algorythm but they were very minor.

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