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Old 03-30-14, 12:52 PM   #71
jeff5may
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Join Date: Jan 2010
Location: elizabethtown, ky, USA
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Spring update:

The unit has been slaving away all winter, saving me money. There are a few issues that I have decided to live with until the weather warms up. We are in the "swing" season now, where the unit sometimes provides heating and sometimes cooling. Regardless of operating mode, the unit consumes 1100 Watts when running. With a compressor rated at 15000 btu, it should run around a COP of 4, not bad for a hacked unit running on bernz0matic propane. Unfortunately, I do not have a definitive way to measure raw btu output.

The only exception to this operation is during winter operation at low outdoor temps (near or just below freezing). In the range of 25 - 35 degF outdoor temp, the unit frosts up like mad and takes extra time to defrost. Below 25 degF, the unit continues to defrost, but unless it is actually snowing, the unit gets through its defrost cycle in under a minute.

As the outdoor temperature plummets below 25 degF, the unit moves less heat indoors. However, it consumes less power in the process. I imagine the COP of the unit drops faster than the power usage, but the main issue is maintaining "warm enough" air temperature to effectively transfer heat indoors. To combat this problem, I block off a portion of the blower exhaust with a piece of cardboard. The cardboard trick chokes the indoor heat exchanger airflow and raises its output airflow temperature enough to have "warm enough" airflow down to about 5 degF outdoors.

When it gets really cold outdoors, I just shut the unit off. If the temp drops into this range late at night, I don't do it until I wake up the next morning. The unit has become the way I tell whether or not to go out and start my car early on those questionable cold days.

Since last time it was shut off, the kill-a-watt says 331 run hrs and 312 KWH. This was during mostly cold weather, so the overall power usage is running below "normal" temperature range. When temperatures rise, power consumption and btu transfer will tend to follow.

The main issue I have with this unit is that I have to mount the thermostat remotely. In heating mode, the indoor coil transfers heat into the frame of the unit. This heat throws off the thermostat, causing short cycling. Strangely, cooling mode doesn't affect the thermostat. So I just moved the thermostat to the wall a few inches away from the unit. Now, the unit provides much better temperature control.

The other issue is with the whole cardboard method described above. If it had separate fans indoors and out, I could match fan speeds to temperature conditions. Unfortunately, both fans are tied to opposite sides of the same motor. I can live with this for the time being (maybe forever). I don't really see an easy way around this issue to make it automatic.

Besides the few bugs early on, and a few refinements along the way, I am very happy with this unit. It has obliterated my gas bill during the winter, while not adding a noticeable amount to my electric bill.

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