Using Heat pump water heater for basement dehumidification

PC7060

I’m dealing with ground moisture moving through the wall of 1928 section of my house. The moisture isn’t such a issue in the summer when the AC is operating but is a headache in the winter when it tend to condense on the second level (top)  exterior windows.  

I’ve looked into standard dehumidifiers  but not impressed with reliability or the wasted energy. 

I’m considering adding a heat pump water heater plumbed to feed the supply side of the boiler Indirect DHW tank. 

A couple questions have come up as part of the design that I have listed for your consideration. 

1. Can you run the heat pump water heaters in HP mode only?
2. How much moisture will the systems remove relative to a standard dehumidifier?

Thanks
P.C.

EdTheHeaterMan

So a Heat Pump water heater will only operate when there is a demand for hot water. The compressor will send the hot gas into the tank and the liquid refrigerant will cycle back to the evaporator coil and blow cool air into the room where the water heater is located.

A dehumidifier will send hot gas into a coil that will heat the air as it leaves the evaporator coil where it releases the humidity to the cold coils as condensation. This cold air is then heated by the condenser coil and leaves the dehumidifier appliance at about room temperature but much dryer.

Not sure the HP Water heater will accomplish that as efficiently. But you will need to use a lot of hot water to keep the compressor running to remove the same amount of condensation from the basement air. and the air will be somewhat cooler.

Larry Weingarten

Hi, I don't have personal experience with this, but have a friend who did just what you're talking about and the HP actually was more efficient at removing water than a dehumidifier based on energy usage. Still, you won't be needing that much hot water probably, so it will help, but likely cannot do all of the work. About HP only mode, ask the manufacturer. Some models revert to resistance heating when you don't think they should. If you can run in HP mode only, be sure you have a large enough tank to carry you through higher hot water demand periods.

Yours, Larry

jumper

The water heater dehumidifies, if it does, for free. Also cools your basement in summer for free. In winter you pay for that cooling. Now a heat pump pool heater is more interesting especially if it has evap coils for both inside and outside.
But if prime function is dehumidification then modern dehumidifier is more efficient.

JakeCK

I have the exact opposite problem. Basement stays dry and I humidify the house all winter. Easily adding 4-6 gallons a day to keep it between 35-50% humidity. Summer I have to run the dehumidifier non-stop even with ac so it was a double hit to efficiency. A HP water heater excells in that environment. But in your case I don't know if it will work as intended. It will save you money in the summer tho.

jinbtown

Pretty much every heat pump water heater I've seen has "heat pump only" mode as well as hybrid as well as electric only. Never seen one without those three options (plus vacation mode)

I'm dehumidifying my basement with a Bradford White Aerotherm 80 gallon. Doesn't remove a TON of moisture but it dehumidifies even in the winter. Little Giant pump is ALWAYS full. I'm up on a hill so a pretty dry basement to start with.

EdTheHeaterMan

The patent for the first air conditioner granted in 1906 was actual called "The apparatus for treating air". It was the work of Willis Carrier who designer the machine to keep the humidity in a printing shop at a constant 55% all year round. One of the benefits of this summertime "Dehumidifier" was how much cooler the printing shop was in the hot New York summers. No wonder the Heat Pump water heater will dehumidity the room it is in. its evaporator coil is blowing the cooler air into that room and the condensing water just needs to be directed to a drain pipe somewhere. Viola! less humidity.

But I still think a dedicated dehumidifier is a better choice to dehumidify a space. It also reheats the air dry as it leaves the apparatus.

PC7060

@EdTheHeaterMan - thanks for the updates, I’ve put the HP water heater idea on hold. Regarding the dehumidifier; are there any you prefer? Other than one built to last 25 years ago!

EdTheHeaterMan

How bad is your humidity issue? The gallons per day rating is what you are looking for. How large is the room. I don't have a preference on a name brand since I believe that everything like that is made by the same little elf at the north pole and they just slap a different brand name on the front. The larger the unit the more humidity it will remove and the more it will cost to operate. (unless you are using solar collectors) then it's free (if you don't count the cost of the collector).

PC7060

The humidity isn't really that bad. My end goal was to reduce/prevent condensation on second floor exterior windows. It turns as this isn't really practical without reducing humidity to very low levels.

Robert_25

PC7060 said:

I’m dealing with ground moisture moving through the wall of 1928 section of my house. The moisture isn’t such a issue in the summer when the AC is operating but is a headache in the winter when it tend to condense on the second level (top)  exterior windows.  

I’ve looked into standard dehumidifiers  but not impressed with reliability or the wasted energy. 

I’m considering adding a heat pump water heater plumbed to feed the supply side of the boiler Indirect DHW tank. 

A couple questions have come up as part of the design that I have listed for your consideration. 

1. Can you run the heat pump water heaters in HP mode only?
2. How much moisture will the systems remove relative to a standard dehumidifier?

Thanks
P.C.

How do you currently produce DHW? A HP water heater would definitely reduce the humidity level in the basement, but it is hard to say if it would clear up your condensation issue. I think you money would be better spent on some water diversion/drainage.

AdamInEvergreen

Relevant aside: There are 120v heat pump water heaters hitting the market now & next year.
https://cleantechnica.com/2021/11/29/120-volt-heat-pump-water-heaters-hit-the-market-make-gas-replacements-even-easier/

From my brief read and not reading the manufacturer specs they have no heating coil. I would imagine they will dominate a 15amp circuit and you can't run anything else on it. Not a recommendation, just a note.

ethicalpaul

My heat pump water heater doesn't pull a ton of moisture out, I still need my dehumidifier. But it is awesome.

jumper

Efficient dehumidifiers are a relatively easy way to reduce over all energy when A/C is required. Do any incorporate a "subcool/reheat" coil ahead of condenser?

from an ASHRAE abstract:
Newer technologies such as subcool/reheat and heat pipe reheat show promise. These increase latent capacity of cool-ing-based systems by reducing their sensible capacity. Also, desic-cant wheels have traditionally provided deeper-drying capacity by using thermal energy to remove the latent load.(2)

PC7060

Thank for the info.  All interesting

My DHW is supplied using a indirect tank of my ModCon boiler. Works well so daisy chaining hot water heater for dehumidification is over complicating the situation. I’ll just get a standard unit if I decide to reduce humidity. 

Currently the humidity is between 45-54 percent.  Just slightly on high side of comfort range. 

Larry Weingarten

Hi, A comment on the new 120 VAC HPs coming out. They are being designed to use no more than 900 watts, so should be able to comfortably share a 20 A circuit, or maybe even a 15 A circuit.

Yours, Larry

JakeCK

Larry Weingarten said:

Hi, A comment on the new 120 VAC HPs coming out. They are being designed to use no more than 900 watts, so should be able to comfortably share a 20 A circuit, or maybe even a 15 A circuit. Yours, Larry

My 30amp 240v heat pump uses a little less than that now when in heat pump mode. But when the elements come on it uses more than my stove top. How do they manage that on a 120v 20amp circuit? They have to have one mighty small element or its strictly a heat pump unit?

PC7060

Wonder how the 120v unit HP unit would work as indirect tank?  You could set the indirect set temp below the HP temp.  Interesting. 

PC7060

I installed a high capacity consumer grade dehumidifier in the basement recently which has brought the humidity down 10 points into the mid 40 range. System extracts about 2 gallons of water a day which has significantly reduced condensate (70-80%) on the second level windows. 

Basement air quality has also improved too. 

The use of the electric HO water heater would be good option if I didn’t already have a reliable indirect water heating system but would be unnecessarily complex to have both.
Thanks @EdTheHeaterMan, @Larry Weingarten, @jumper and other for steering me towards the simple solution. 

EBEBRATT-Ed

900 watts is only 7.5 amps at 120 volt. So that will require a 15 or 20 amp circuit.

But how much water is that going to heat?

Not much. about 3000 btu

Larry Weingarten

Hi @JakeCK , I'm not privy to what the manufacturers are doing with element sizes. But, if they drew 900 watts, that would be one fifth the size and speed of conventional elements, so it would be good not to go with the smallest tank available!

Yours, Larry