Air-to-water heat pump might be fixed

May 16, 2010 · Posted in Uncategorized · 6 Comments 

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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Air-to-water heat pump failure

May 16, 2010 · Posted in Construction, Lessons Learned from a Green Building Project · 3 Comments 

My family built a new home in 2004, and given my long professional background in energy efficiency, it was only natural to include as many energy features as we could afford. I’ve always recognized that home efficiency starts with a tight, well-insulated building envelope. We selected a general contractor that impressed me with his knowledge of building science and a long history of building homes ahead of the curve. Although not a builder myself, I’ve worked with them for many years. I’ve always believed that a builder develops a “system” that works for him or her, and that as a client I would be wise to adopt that system. In this case the system included  hydronic radiant floors driven by an air-to-water heat pump. When our house was built this contractor had already installed several of these systems with good results. Ours was to be the first of many problematic systems over the next several years.

Repeated failures and costly repairs over the last four years have prompted us to seek estimates for a replacement. We might consider another brand of air-to-water heat pump (aka reverse cycle chiller) or we may simply convert the system to a gas-fired tankless water heater.

(click for a larger view)

The original system (above) was installed in late 2004 by our general contractor. The system is a standard York heat pump mated to a heat exchanger made by Aqua Products.

A Good Beginning

The first heating season was trouble free and the system performed very efficiently. The coefficient of performance was measured 3.5 at 49°F. Even when temperatures dropped to the single digits, the system was able to heat the 1800 sq. ft. home without backup heat. After that first heating season we were pleased and optimistic.

Trouble Brews

In November of 2005, the system died. During this time, the house was heated by a single 4.5 KW electric element in the standard electric water heater that serves as the storage tank. In a perverse way, this was instructive. We were able to measure how much heating energy is required without the extra efficiency of the heat pump.

We called in a well-regarded heating contractor. Several months passed as the system was diagnosed and finally York agreed to provide a replacement compressor, while the local distributor paid the labor costs to install it. The work was finally completed in April 2006, two weeks before we shut the system down for the season. While the system is capable of mechanical cooling, we seldom use it. The new compressor performed well during the following heating season, and again we were optimistic.

Replacing the York compressor(click for a larger view)

Replacing the York compressor(click for a larger view)

Another Compressor Fails

The system stopped working again in November of 2007 due to a failed compressor. This time York agreed to replace the entire outdoor unit with a highly efficient member of the Affinity line. We paid our heating contractor for the labor. The work was completed in February of 2008. For the second time, the system was out of commission during the coldest part of the winter.

New outdoor unit(click for a larger view)

Just a week later, this new unit stopped functioning during a moderate cold snap — the temperature dropped to the mid 20s. York’s factory representative was in town to meet with a group of HVAC contractors who had been experiencing problems with air-to-water heat pump systems. He dropped by to take a look and declared that all was well.

In December 2008, about six weeks after the system began operating for the season, the system began to cut out. The diagnostic code indicated high discharge line temperature. The York factory representative again visited the system along with local HVAC technicians. He suggested that the liquid line sensor be moved to a different location. That change has not prevented repeated cut outs, all showing the same high discharge line temperature code. Actually, it seems that the cut outs are more frequent now.

All these problems have occurred within the York heat pump, so we have asked that York cover the materials and labor to fix it. Citing the warranty, which does not cover labor, York has offered only to supply replacement parts.

We have decided not to invest any more of our own money in the York/Aqua Products system, and have started to research a replacement system. We might consider other reverse cycle chillers now available from Daikin and Unico. On the other hand, we may just install a gas-fired tankless water heater.

(Note: This post was originally written in late 2009. Since then there has been a new development and the heat pump may be fixed.)

— Bruce Sullivan

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Energy conservation first then solar: the sequence for success

May 9, 2010 · Posted in Construction, Lessons Learned from a Green Building Project · Comment 

When we built the house in 2004, solar electricity (photovoltaics) was too expensive for us. Since this was new construction, we were able to focus on the most cost effective measures first. I think we succeeded for the most part, although I’ve learned a lot in the last six years and would do things differently. One thing we did get right was the concept of focusing on conservation first. The building site and orientation capture passive solar heat. Because passive solar is mostly a design issue, there is very little direct cost. Just use your noodle and make the right design decisions. The building shell is tight and well-insulated. Spray foam insulation was spendy, but performs very well and never wears out. It was a good investment given the choices at the time, although it’s one of those things I might do differently. Choosing conservation and passive solar was the obvious choice: a no-brainer.

solar water heating collectors and photovoltaic modules

Solar water heating collectors and PV modules share the roof, but they were installed years apart.

But I wanted to go further, so the next step was some kind of renewable energy system. I had already experienced the joys and savings of solar hot water on a previous house, so I knew I would like it. Plus it’s generally accepted that solar water heating captures more energy for each dollar invested. The actual performance is determined by the local climate (availability of sun) and the equipment selected. In central Oregon, the Sun Earth solar system that we installed is expected to generate 3100 kWh per year of energy in the form of domestic hot water. The performance of solar water heaters varies quite a lot. Performance information is available from the Solar Rating and Certification Corporation (SRCC).

Before incentives, the solar water heater would cost us about $6000. Back in 2004, a photovoltaic system capable of generating the same amount of energy (2.2 kiloWatts) would have cost more than $25,000. So, it made sense to install the solar water heater first and wait for PV prices to come down. Now it was time to think about making the house PV ready. I wanted to do everything possible to prepare the house for a smooth PV installation when the time was right.

The site selection and building orientation that work so well for passive solar also give us a large area of unshaded south facing roof. There’s an old rule of thumb for the optimum angle of a solar collector that says the collector angle should be equal to the latitude. That would be 44°N here. The roof pitch is 6-in-12 or about 21°. Most experts agree that the angle penalty is small, especially because winter sun which benefits from the steeper pitch is not as plentiful anyway. So, my roof is a bit flatter than optimum, but the collectors lay flat and look good.

The solar water heating collectors were positioned off to the side, almost directly above the storage tank in the garage. That left a large open area for PV modules. We relocated a couple of plumbing vents so they would not interfere. Flues, chimneys and surface mounted roof vents would be other things to look for, but we didn’t have any of those. But it’s not just physical obstructions that could foul up a PV installation. Shade is the devil. Even a small amount of shade on a typical PV array can kill production. You certainly don’t want architectural elements, such as dormers or chimneys, sabotaging your PV system down the road.

You also must anticipate the space needed for other system components, including the inverter, meter and disconnect switch. These elements are generally located next to the electric service panel or breaker box. In my case, this all fits within a 3-foot by 3-foot area. One often recommended element is an electrical conduit leading from the electric service panel to the roof. We decided not to spend money on the conduit, because it could easily be run up the side of the house. If a conduit is included in the PV-ready package, you will have to be very explicit about the location of the modules and the wiring.

By 2009, the economics of photovoltaics had changed considerably. State and federal income tax credits along with electric utility incentives were higher than ever. On top of that, the market for PV modules found itself with a supply glut that drove prices to unprecedented lows. This combination of factors brought the ultimate price of a 2 KW PV installation to below $1000. It was time to move from PV ready to PV installed.

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