Replies

1. 
   BillHartmann | Sep 19, 2009 11:58pm | #1

   VATom has been doing that for a long time. He has need for year around dehumidification and that is part of it.

   .
   William the Geezer, the sequel to Billy the Kid - Shoe
1. 
   ted | Sep 20, 2009 01:08am | #3

   Dehumidification from the output of the heat pump?
   I wonder if the exhaust were piped into the HVAC system if the cooling coils in the air handling unit would zap some of that moisture out?

1. 
   BillHartmann | Sep 20, 2009 01:34am | #4

   I am not sure what you mean by the exhaust.Any refrigeration system has a 2 coils, a compressor, and a refrigerant. They system removes heat from one coil, making that one relatively cold and moves to the 2nd coil, making that relatively hot.Bye using different size coils, different size of expansion orifices, and refrigerants you can make it work for different temperature ranges.That basic system is used for freezers, refrigerators and the system that you brought up.Now whenever the cold coil is below the dewpoint the water condense and it remove moisture and if cold enough will freeze. That is my refrigerators have defrost cycles and air conditioners have condensate drains.A dehumdifier is basically the same, except that both the hot and cold and coils are in the same environment. And it is optmised for removing moisture rather than moving heat from one place to another.What is commonly called a heat pump is an air conditioner with a reversion valve so that in addition to move in heat from the inside to the outside. In heat pump mode the flow of refrigerate is reversed to move heat from the outside to the inside.In general the capital equipment cost of a system like you mentioned is high enough that they usually are not cost effective even if they use little energy.They are cost affect when they can use reject heat from another system that is already required. Dan mention ones that use the rejct heat from milk coolers. And I mention one that is used because dehumidification is required.And they are sometimes added to AC system in the south where the AC might run 9-10 months of the year. I think that they are call desuperizators or something like that..
   William the Geezer, the sequel to Billy the Kid - Shoe

1. 
   ted | Sep 20, 2009 04:58am | #5

   I didn't think the cost was so out of line for that particular unit ($600.00). And if the water heater uses electric heating elements (like mine) I thought the payback might be as little as two years. I can see the benefit of such a system during the summer months when cooling a structure is an issue and the Airtap is using warm indoor air and putting out cool air to help cool a space and help reduce the amount of energy an AC would use. In the winter I'm not so sure if the amount of energy needed to reheat the cool air would offset any energy savings from the Airtap.
   I just installed a high efficiency heat pump this summer to heat and cool our house so I'm familiar with the way such a system works.

1. 
   DanH | Sep 20, 2009 06:24am | #6

   Actually, if you're replacing an electric resistance unit, and the house heat is natural gas, it's likely that it would be a money-saver even in the winter.
   As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz

2. 
   BillHartmann | Sep 20, 2009 03:19pm | #7

   Yes, but for the less cost you can just replace the WH is a gas unit..
   William the Geezer, the sequel to Billy the Kid - Shoe

3. 
   DanH | Sep 20, 2009 03:34pm | #9

   IF the location for the heater is acceptable for a gas unit. In our case, eg, there's no way put in a legal flue.
   As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz

4. 
   florida | Sep 20, 2009 03:52pm | #10

   They are fairly common here in south Florida. My house had one that died before I bought it so I took it off. The difference is that down here they are mounted on the outside wall next to the compressor and piped to the water heater. My A/C guy offered to install one for $900.00 several years back and said his had reduced his hot water electrical usage to near zero.

5. 
   Junkman001 | Sep 20, 2009 06:18pm | #11

   What about a power vent?

    

   MikeInsert initially amusing but ultimately annoying catch phrase here.

6. 
   DanH | Sep 20, 2009 09:48pm | #12

   Can't power vent within N feet of an operable window, and too many windows.
   As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz

7. 
   BillHartmann | Sep 20, 2009 10:58pm | #13

   "Can't power vent within N feet of an operable window, and too many windows."Actually it is B and not N (on the vent clearances charts).I was concerned about that with a relatively small distance between the chimney, and you have clearance from and inside corner, and an operable window, which is never operated. And I wanted to vent a furance, possibly two, and a WH.I had also remembered ft. But there id chart in the furnace manual and one for the WH and most of the numbers are the same as it is based on the national codes and standard and not on manufacture recomendations (except for a few minor differences).Clearance to the side or below for any operable door or window is 9" if less than 50,000 BTU or else 12", for a 2 pipe installation.However, for a single pipe it is 4 ft. That make absolutely no sense. And there are two pipe power vents available. Go to State WH and look find a power vent model and then look up the installation instructions. It with have that chart in it..
   William the Geezer, the sequel to Billy the Kid - Shoe

8. 
   DanH | Sep 21, 2009 06:14am | #14

   Our local code guys allow a furnace to be vented close to windows on the theory that the windows will be closed in the winter. But a water heater must meet the distance restrictions.
   As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz

9. 
   ted | Sep 20, 2009 03:31pm | #8

   Yes, I have an electric water heater. ANd my HVAC system is an high efficiency electric heat pump.

2. 
   DanH | Sep 20, 2009 12:16am | #2

   Been around for 20-30 years. Makes sense in some contexts. Dairies use a version that combines a hot water heater with a milk cooler.

   As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
3. 
   Clewless1 | Sep 21, 2009 03:30pm | #15

   As some eluded to, it may have some applications, but you are dumping cold air into the house, so if you need to heat that back up, it's likely an energy loser. If you use 3413 Btu (one Kwh) to transfer energy to the water, you remove say 1000 Btu into the house which will take say 1200 Btu of gas to heat up.

   Probably the best application is a warm humid cooling climate, then as one poster said, you dehumidify the air in the house. I'm sure that is the likely application for this. I surmise it might be expensive, relatively speaking, unless you have a large hot water demand.

   oops ... math error ... I mean 10,000  Btu (of cooling) transferred into the house w/ one kwh (3,413 Btu) and then use 12,000 Btu of gas to heat it back up.  I was just checking to see if you guys caught it ... and you didn't. HA ;)

   
   

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   Edited 9/23/2009 8:00 am ET by Clewless1

1. 
   ted | Sep 22, 2009 01:51am | #16

   That was my thinking too. However I can see it working 7-8 months out of the year when we aren't heating our house. During the heating season I can see turning the Airtap off and using the electric resistance. In this fashion the payback would be drawn out longer.