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Old 12-23-12, 04:39 AM   #1
launboy
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Default Q&d ashp

Problem: I have a garbage picked dehumidifier, a month off of school, and some ambition.

Solution: Build myself a quick and dirty window shaker heat pump.

My first idea for this dehumidifier was to build a mini-chiller to use to use with a remote fancoil, built from a 10" fan and the condensing coil from the other dehumifier i garbage picked with this one that had no charge. Plans changed when I realized it would be difficult to hide while dealing with the exhaust air, and noise.

Decided instead to use a 7 gallon container with ice water circulated through my home made fancoil for dorm cooling instead. Worked well if it was pointed at you. Made sleeping much more pleasant.

Anyway here's that:
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Started bending things around and this was my prototype. That white fan is the one I used for my fancoil. didn't move nearly enough air through this coil.
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Final design. After much fanagaling of piping to get it to reach where it needed to and line up like I wanted it to here it is. All that's left to do is secure it to the base I have, and put an enclosure around it.
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Currently it's running in my basement, keeping me warm, which is about 59*F, drawing 470w(compressor) + 60w(fans) = 530w, putting out 96*(37*dT) air on the hot side and 42*(18*dT) air on the cold side. I wish there was an easy way to know how any BTU's of heat I'm actually putting out with this thing. I measured the CFM of the indoor(hot) fan with a 30 gal garbage bag and a stopwatch and got 96 CFM, though I'm not sure how accurate that is.

Notes: I originally had the fans switched around with the blower(from a 5000 btu window shaker) on the condensing side and the axial(original to dehumidifier) on the evap. This lead to about 74*F discharge temps hot side, aka not warm feeling when blowing on you, and cold side coils that froze even in 60* basement air. I switched these around to achieve a lower dT on the evap to reduce frosting/freezing, which it has, they don't even get cold enough to condensate where the air is passing over them, and to achieve higher discharge temps on the condenser side, so it feels nice to those who feel it.

I don't know how many BTU's this thing puts out at room temp, at actual outdoor temps, or if it's even anywhere near efficient, but I know it's a fun little project that gives me something to do. The best test I'll be able to do is to heat a small room with a space heater and track the temp vs/ time, and heat it again with this hp, and compare, unless someone has a better idea?

Adam

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Old 12-30-12, 01:56 PM   #2
Daox
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Any updates on this project Adam?
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Old 01-11-13, 12:23 AM   #3
launboy
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Yes there is actually. Finished it, mostly anyway, and tried it out. Unfortunately defrost didn't happen. On my Hot Tub Heat Pump I could turn it off and the heat from the hottub water and in the compressor (I assume) would migrate to the evap and melt the frost. This one did not do that. Once it frosted up, it was game over until I brought it back inside.

Examining our electric bill today I did a little math and I would need to achieve a COP of 3, conservatively, to just break even with the cost of nat gas here. If I ignore the tax and basic hook-up charge on each, which is about the same amount, it works out to $.132 /kwh electric, and only $.018 / kwh equivalent for gas, because hook up fee and tax costs more than double what the gas for that month costed.

The fact that I need a COP of 3 to break even here, makes heat pumps much less appealing in this area, especially in the winter.

Adam
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Old 01-11-13, 01:24 AM   #4
BradC
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We have the same "problem" down here. While it's much "greener" to use a reverse cycle A/C (heat pump for you Northerners) it works out *much* cheaper to use natural gas heating if you are in any area serviced by a gas supply (most metro areas anyway).
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Old 01-11-13, 01:50 PM   #5
AC_Hacker
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Quote:
Originally Posted by BradC View Post
...it works out *much* cheaper to use natural gas heating if you are in any area serviced by a gas supply (most metro areas anyway)...
Yeah, it varies so much locally...

Here is a splendid calculator to easily calculate the differences both in cost and also in CO2 emissions for your particular location. The calculator includes the typical CO2 output for a coal powered electric plant.

The happy optimum is when both cost AND CO2 are minimized by the same choice.

Best,

-AC

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