# Thread: Heat pump can dehumidify?

1. ## Heat pump can dehumidify?

Anyone ever built a heat pump before?

I'm thinking of taking our old dehumidifier(which still works, just kept freezing up when it was in our basement) and using it as a HP for the hot tub. I already used it as a portable A/C and it does do that, it's just not big enough for what I'd use if for(pop up camper) at only around 6000 BTU. I noticed though, while taking temps. on the coils, that the condenser coil ran around 140. Seems like a great way to keep the hottub hot on those cloudy days. If the thing ran at 100% efficiency I'd gain around 3*F an hour. Even at only 66% that would be 2*F an hour which would heat the tub(albeit slowly) or maintain it easily.

Why don't I just use the resistance heat in the spa pack you ask? Because it's inneficient and SOO SLOW. I only have 120v out back so I only have 1.375Kw of heat. This means that for 1500w(1.5Kw) I get about 3000 BTU/Hr vs. the Dehu. HP which would give me(hopefully) about 5000 BTU/Hr but drawing only about 700w(.7Kw).

Doing a bit of figuring I end up with the numbers below...

Amount of Electricity used to produce a certain number of BTU.
.5w = 1 BTU ..... Resistance
.14w = 1 BTU ... Heat Pump
.5w = 3.6 BTU .. Heat Pump
1000w = 2000 BTU ... Res.
1000w = 7200 BTU ... HP
*** Our Electric rates are about \$.10 KwH***
Theoretically to heat the tub 10*F it should take about 21,000 BTU.
20,750 BTU x .0005 Kw x \$.10 KwH = \$1.04 ...... Resistance
20,750 BTU x .00014 Kw x \$.10 KwH = \$0.29 .... Heat Pump

I believe that gives my Dehu. HP a COP of 3.6. (not sure if that's how it's figured) And that's figuring 83% efficiency on the HP. Seems like a good deal to me!

Obviously the Dehu. would be plugged into a GFCI outlet and I wouldn't use it when people are in the tub(Just in case) so nobody will get electrocuted if something leaks/shorts.

Does my math sound right? Anybody see any obvious holes in my plan?

2. ## Re: Heat pump can dehumidify?

Your 6000 btus of heat transferred per hour is equal to 1.8 kw of electric resistive heat per hour.

Not much difference compared to what you have now.
It would heat only slightly faster, however the biggest advantage assuming you could do this is that your dehumidifier would consume approximately 1/3rd the electricity compared to your resistive heater.

Good luck

Lee

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