Heat pump water heaters, where does the heat come from to transfer.

hot_rod

If the hpwh is located in a basement near a conventional cast iron boiler, the jacket and piping loss is the source. Sometimes considered spare or surplus heat. It typically finds a way out of the building in an uninsulated, unsealed basement. May as well put it to use.

If you have a well insulated home heated by a heat pump, and a hpwh, cascading heat pumps🤔, the math gets a bit fuzzy.
In this example the hpwh cop actual decreases as the space is warmed by the heating systems heat pump

So consider where the heat energy comes from that the hpwh transfers into the tank, and what effect the 46 degree discharge air has on the enevelop.

Mad Dog_2

Always thinking....VERY good 👍.   Mad Dog

EBEBRATT-Ed

I suppose the HPWH air could be ducted from the outside but would have a condensation issue and would have to be well insulated.

Same issue with a refrigerator or freezer. They help heat the space in the winter but become part of the AC load in the summer.

JakeCK

hot_rod said:

If the hpwh is located in a basement near a conventional cast iron boiler, the jacket and piping loss is the source. Sometimes considered spare or surplus heat. It typically finds a way out of the building in an uninsulated, unsealed basement. May as well put it to use. If you have a well insulated home heated by a heat pump, and a hpwh, cascading heat pumps🤔, the math gets a bit fuzzy. In this example the hpwh cop actual decreases as the space is warmed by the heating systems heat pump So consider where the heat energy comes from that the hpwh transfers into the tank, and what effect the 46 degree discharge air has on the enevelop.

I could have sworn I read somewhere that overall the efficiency of the house as a system is still greater then either one of those heat pumps by themselves. Kind of like a two stage heat pump. 

I could be mistake however, or the source was simply incorrect. 

SteamingatMohawk

So, the question is how many BTU/hr are removed from the basement to heat the water and what effect does that have on the temperature in the basement. I have often wondered about it, but never bothered to look at the numbers.

ethicalpaul

EBEBRATT-Ed said:

I suppose the HPWH air could be ducted from the outside but would have a condensation issue and would have to be well insulated.

The Rheem ones come ready for ducting. They have a condensation drain line, condensation is a concern even in a normal basement without using the ducting. In the winter my condensation line is dry, but in the summer it drips all season into my slop sink. No biggie.

I will repeat this for the nth time: the cooling effect in my basement is not noticeable. My basement has uninsulated concrete block walls and the heat loss through these GREATLY outweighs the cooling effect of the HPWH.

If I didn't know it was there, I'd never be able to tell it's there.

hot_rod

ethicalpaul said:

EBEBRATT-Ed said:

I suppose the HPWH air could be ducted from the outside but would have a condensation issue and would have to be well insulated.

The Rheem ones come ready for ducting. They have a condensation drain line, condensation is a concern even in a normal basement without using the ducting. In the winter my condensation line is dry, but in the summer it drips all season into my slop sink. No biggie.

I will repeat this for the nth time: the cooling effect in my basement is not noticeable. My basement has uninsulated concrete block walls and the heat loss through these GREATLY outweighs the cooling effect of the HPWH.

If I didn't know it was there, I'd never be able to tell it's there.

Calm down Paul🤓, it not just about your basement. I’m just explaining the concept of “pumping heat”
You have an ideal installation and location, not everyone does. It’s nice to hear different views.

ethicalpaul

Sure no sweat Bob I wasn't trying to trash anyone's views, sorry if it came off that way.

But I do see a lot of hand wringing around here on this topic, and I'm just trying to say "it's no big deal".

My installation and location aren't ideal, they are just typical. It's just a basement like anyone else's. But based on what I've seen, these HPWTs would work fine in any basement. I think they would work fine in many semi-outdoor situations too, like how down south they sometimes put their mechanicals in an adjacent shed or something. Anywhere you'd put a gas or electric water heater.

Derheatmeister

Warmer Clima situation:
My Brother which has an unconditioned garage near Boca Florida just had a HPWH installed 2 weeks ago...One of benefits is that cooling down the garage Via the HP will most likely reduce his AC load.
Win,win situation.

Jamie Hall

Not really all that hard to calculate the heat involved, in BTU. Remembering that a pound of water takes 1 BTU to change 1 degree F.

About 75 to 80 percent of the heat will be drawn from the surrounding air -- but unless the domestic hot water load is really huge, it's surprisingly little heat. For 30 gallons per day hot water, you're only looking at 700 BTUh or so. We often th8ink of a water heater taking a lot of heat, and in the case of an instantaneous unit that is so -- but not for all that long at a time.

hot_rod

In HP mode only, recovery can be a bit of a wait with that low btu/hr input of a HP

If you want DHW now, and lots of it, 4 gpm, the number gets big.

A simple look at a 4 gpm flow of 45° incoming elevated to 122°
500 (f) (∆T)
500 X 4 X 77= 154,000 btu

I like the concert of HPWH, as long as you look at the big pic. The 120V versions can be workable in many homes.

Derheatmeister

hot_rod said:

In HP mode only, recovery can be a bit of a wait with that low btu/hr input of a HP

If you want DHW now, and lots of it, 4 gpm, the number gets big.

A simple look at a 4 gpm flow of 45° incoming elevated to 122°
500 (f) (∆T)
500 X 4 X 77= 154,000 btu

I like the concert of HPWH, as long as you look at the big pic. The 120V versions can be workable in many homes.

Yes...The "DHW Now" situation can be a little tricky,lessen the COP/Efficiencies of these Units.
These systems work great if you can wait until the end of the day to do your Dishes/Laundry/Take showers which is very simular to a Solar system..Most of the newer models have abilities to be programmed for this/Communicate..

An other way to utilize HP type Water heaters would be to interface it with latent heat storage such as the IVT Latento reverse indirect tanks https://ivt-group.com/en/produkte/latento-solarsystem/...

Jamie Hall

hot_rod said:

In HP mode only, recovery can be a bit of a wait with that low btu/hr input of a HP

If you want DHW now, and lots of it, 4 gpm, the number gets big.

A simple look at a 4 gpm flow of 45° incoming elevated to 122°
500 (f) (∆T)
500 X 4 X 77= 154,000 btu

I like the concert of HPWH, as long as you look at the big pic. The 120V versions can be workable in many homes.

Quite. The real downfall of both heat pump water heaters -- and the imitation on so-called instantaneous ones. The saving grace is that that load usually doesn't last all that long.

EBEBRATT-Ed

Just like an air conditioner the heat of compression is added to the heat put into the DHW, which is about 25% of the heat. So in reality the HPWH lets say takes in 75% of it's heat from the surrounding air (cooling the air) and picks up the other 25% or so from the compressor.

Hot_water_fan

I'm intrigued by Rheems 120V 12,000 btu heat pump water heater. It's close to a regular electric tank's output, which I found works fine for my needs. But pulling 8,000 btu/h out of a basement might be noticeable!

Jamie Hall

Hot_water_fan said:

I'm intrigued by Rheems 120V 12,000 btu heat pump water heater. It's close to a regular electric tank's output, which I found works fine for my needs. But pulling 8,000 btu/h out of a basement might be noticeable!

It would, if it were on all the time -- but unless you are running a laundromat or have four teenage girls, that 8.000 BTUh is only going to be running an hour or two each day, so it's not as bad as it sounds!

JakeCK

My experience with mine has been that the additional cooling and dehumidification during the summer months largely offset any increase in electric usage after switching from a NG. My year over year energy consumption did not increase despite it using roughly 110kwh a month.

Does it run enough to make enough of a difference that can be felt? No, not really unless you are standing in front of it. But a BTU is a BTU and a watt is a watt. Any decrease in the run time of my dehumidifier in the middle of July pays back double. Once for not having to run to remove the moisture, and second for the AC upstairs not having to remove the heat generated by that dehumidifier. 

EdTheHeaterMan

@hot_rod all you need to do is look at my old post about how cast iron holds the heat for your answer. https://forum.heatinghelp.com/discussion/comment/1709810#Comment_1709810

jumper

Unfortunately everybody installs unitary equipment these days. Actually for a very long time. Instead of a building a system.
When I was a student working for a supermarket refrigeration company I suggested that one condenser be located inside the store to be used when weather was extremely cold. Bosses praised my idea but I haven't seen it implemented anywhere in decades since. With heat pumps for DHW or swimming pool ideal is dual evaporators. One inside when A/C is required and another outside when it's warmer there than inside.

ChrisJ

Paul doesn't use much hot water for a few reasons...

My 40,000 but/h heater runs no less than 2 hours per day.  That 80,000 would come from somewhere else and that's significant in the winter.

pecmsg

jumper said:

Unfortunately everybody installs unitary equipment these days. Actually for a very long time. Instead of a building a system. When I was a student working for a supermarket refrigeration company I suggested that one condenser be located inside the store to be used when weather was extremely cold. Bosses praised my idea but I haven't seen it implemented anywhere in decades since. With heat pumps for DHW or swimming pool ideal is dual evaporators. One inside when A/C is required and another outside when it's warmer there than inside.

Isn’t that what’s done today with Rack Systems? 3-5 compressors sharing the load depending on the actual load. First on first off. 

jumper

@pecmsg Yes, with common refrigerant line they can and often do have multiple condensers. But I suggested locating one (or some) condensers inside store. Instead you see louvers for frigid air.