Air-to-water heat pump might be fixed

May 16, 2010 · Posted in Uncategorized

The air-to-water heat pump saga has played out over six years. It has involved two major equipment replacements, a dozen service calls along with many hours of hassle and uncertainty. The entire story appears in a previous post. That story ends last December with a heating system that was utterly unreliable. I started collecting bids to replace the system with another brand of air-to-water heat pump or a gas-fired tankless water heater.

When I finally decided that there was nothing to lose with the heat pump, I decided to tinker with it. I had noticed that the system always shut down during the heating cycle. (A number of other York air-to-water heat pumps were failing in my area, but they were cutting out during the defrost cycle.) The diagnostic code consistently showed the high temperature discharge error. Each and every time this happened there was frost on the coils. The factory rep and local technicians dismissed the frost, because it was light. They were accustomed to seeing much thicker frost on heat pumps without adverse effects. Nevertheless, this bothered me. I began to correlate the failures with specific weather conditions and confirmed that the failures always occurred when outdoor relative humidity was 85 percent or above. The heat pump operated without apparent problems to temperatures as low as 15°F as long as the humidity was low, but it would ice up and cut out at 34°F if the humidity was higher than 85 percent.

On one of his many service visits, I asked the factory rep to show me how to engage the defrost cycle manually. He pointed out the test contacts on the defrost control circuit board. Using the blade of a flat screwdriver, I could span the two contacts and force the system into defrost mode. Now I had a way to test my hypothesis that the heat pump was not defrosting properly. It was mid-December and weather conditions were ripe for the system to fail. I watched the system closely and engaged the defrost whenever the frost was thick enough to block the space between the evaporator coil’s fins. This turned out to be three to four times a day. With regular defrosts, the heat pump continued to operate for a couple of days. When I stopped the manual defrost regimen, frost accumulated on the coils and the heat pump shut down. Every time the diagnostic code showed high discharge temperature. I was convinced that more timely defrost was the answer. Now what?

I remember the factory rep describing York’s sophisticated defrost programming, so I looked up the service manual for my model on the Web. I found that this line of York Affinity heat pumps shared a common control board. The appropriate defrost program or “defrost initiation curve” is set by positioning a jumper on certain pins on the board. My outdoor unit is four tons and the jumper was set according to these instructions in jumper position four. Since that wasn’t working, I thought I’d just try something different and see what happened. I simply moved the jumper to position three for a three ton heat pump.

The heat pump now defrosts regularly and the coils remain clear. Since making this change in mid-December, the system has cut out only once. That happened a day or two after the adjustment. We have now made it to the end of the heating season and there has never been another equipment shut down, despite many long stretches of time when conditions were ripe for failure. The heat pump has operated through it all. I’m ready to declare short term victory, but have no idea how this will work in the long run or if this solution puts excessive strain on the equipment. Frankly, I don’t care about the equipment, because it was simply unreliable and now it works.

Despite my six-year ordeal with the York equipment, I’m still a supporter of the concept of an air-to-water heat pump combined with a hydronic radiant floor. I’ve talked with others that have installed both Daikin and Unico equipment, and the early reports are positive.

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Comments

6 Responses to “Air-to-water heat pump might be fixed”

Jeff Weik on June 2nd, 2010 8:53 am

I am looking at this idea for my house. I have a radiant floor heating system and would love to heat the water for it with a heat pump. I’ve looked at the Daikin units, but they are prohibitively expensive, and don’t even qualify for the Federal tax credit. I was planning to use one of the high-efficiency Nordyne iQ Drive heat pumps, coupled with a refrigerant-to-water heat exchanger coil. I would like to get more details on your system design and controls.

Please contact me. Thanks! Jeff Weik
Bruce Sullivan on June 3rd, 2010 9:42 pm

I spoke with a Daikin rep last week. They are collecting the documentation necessary to qualify for the tax credit. If you want to move ahead right away, you might contact Aqua Products . Their reverse cycle chiller can attach to any standard unitary heat pump. Perhaps you could arrange a custom application with the Nordyne outdoor unit.
Mike O'Brien on August 9th, 2010 5:44 pm

Thanks for the update, Bruce, and nice sleuthing! I got a quote of $22,000 for a Daikin Altherma system. I don’t really understand why the price is so high. Even with the 30% renewables tax credit it will be an expensive option.
Bruce Sullivan on August 14th, 2010 3:34 pm

It wasn’t so much sleuthing as “nothing to lose” experimentation. We’ll see if it holds through another heating season. My sense is that Daikin is targeting ground-source heat pumps as their competition. I’m told that the Altherma will cost about the same as the ground-source minus the ground loop, but will deliver comparable performance. It’s too bad that any kind of hydronic heat is still considered a premium product.
Jim on September 13th, 2010 8:10 pm

Take a look at Aermec’s air to water heatpumps. Self contained like Altherma and they have been building them since the 80s. We have had great success.
Bruce Sullivan on September 13th, 2010 9:06 pm

Jim,

I wasn’t aware of Aermec, but it looks very interesting. Here’s a web site for more information. http://www.aermec.ca