Will my HPWH (heat pump water heater)

hot_rod

Heat or cool my shop:) Design day of 5°, I need about 28,000 btu/hr.

This freight damaged tank came my way a week or so ago. I disassembled and straightened the jacket, re worked the wiring on the control board and low and behold after a 20 minute self diagnostic it fired off.

In efficiency mode this 80 gallon tank takes about 12 hours to raise the temperature to 120F from 55F, in a 54° space of about 11,000 cubic feet of shop. The manual claims about 1/2 ton of cooling effect.

In the process it belches 48° air into the space, a bit noisier compared to a mod con by about 10 decibels.

It draws just under 1.5A when running in heat pump only mode. My PV array was cranking out about 2800W during part of the run. Under favorable conditions it could run a 3 or more COP, according to the manufacturer.

So, if time is on your side, and you have a good operating space, under 120F SWT it can be a cost effective means of DHW.

As far as a radiant source of 110F???

ChrisJ

12 hours...
I'm guessing 38 degree water is even more fun.

Jamie Hall

Lett's see here... cranking up the calculator (there was a time I could do this holding numbers in memory. Must be getting old). That temperature rise is somewhere around 41,000 BTU. In 12 hours, works out to about 3,500 BTUh. Which, as an aside, indicates a pretty good COP -- 1.5 amps is only about 200 watts, so your getting a factor of about 5 there. Not bad.

However...

3,500 BTUh is a pretty far piece from 28,000 BTUh.

Worse, the heat pump water heater can't be in the space being heated...

Zman

I must be missing something. Is the water heater taking heat from the air in space and dumping it in the slab in the same space?
Sorry, first cup of coffee....

mattmia2

Zman said:

I must be missing something. Is the water heater taking heat from the air in space and dumping it in the slab in the same space?
Sorry, first cup of coffee....

no, no, i've read it a couple times and am having trouble figuring out how this isn't an electric resistance heater too...

ChrisJ

Jamie Hall said:

Lett's see here... cranking up the calculator (there was a time I could do this holding numbers in memory. Must be getting old). That temperature rise is somewhere around 41,000 BTU. In 12 hours, works out to about 3,500 BTUh. Which, as an aside, indicates a pretty good COP -- 1.5 amps is only about 200 watts, so your getting a factor of about 5 there. Not bad.

However...

3,500 BTUh is a pretty far piece from 28,000 BTUh.

Worse, the heat pump water heater can't be in the space being heated...

It would be interesting if it was. We've seen weirder things.

EBEBRATT-Ed

I guess time will tell about the longevity of the HPWH versus the expense of cost and installation

mattmia2

EBEBRATT-Ed said:

I guess time will tell about the longevity of the HPWH versus the expense of cost and installation

how has the longevity of anything else using small copper tubing gone for the past 15 years or so?

Solid_Fuel_Man

The best thing I see about heat pump water heaters is stick them in a hot Boiler Room. Then that nice hundred degree room gets cool off a little bit and you get almost free hot water

ChrisJ

Solid_Fuel_Man said:

The best thing I see about heat pump water heaters is stick them in a hot Boiler Room. Then that nice hundred degree room gets cool off a little bit and you get almost free hot water

Except you're sucking the heat out of the room causing the boilers to give off more.

I don't know how noticeable it'd actually be, but nothing's free.

hot_rod

mattmia2 said:

EBEBRATT-Ed said:

I guess time will tell about the longevity of the HPWH versus the expense of cost and installation

how has the longevity of anything else using small copper tubing gone for the past 15 years or so?

The copper tube HX is wrapped around the outside of the tank, I suspect it is in a less harsh environment compared to say an AC condenser coil outside, so it should last a good while.

hot_rod

ChrisJ said:

Jamie Hall said:

Lett's see here... cranking up the calculator (there was a time I could do this holding numbers in memory. Must be getting old). That temperature rise is somewhere around 41,000 BTU. In 12 hours, works out to about 3,500 BTUh. Which, as an aside, indicates a pretty good COP -- 1.5 amps is only about 200 watts, so your getting a factor of about 5 there. Not bad.

However...

3,500 BTUh is a pretty far piece from 28,000 BTUh.

Worse, the heat pump water heater can't be in the space being heated...

It would be interesting if it was. We've seen weirder things.

It's 48 outside today and sunny giving me some solar gain, that 3500 btu/hr will cover the load today.
The heater is inside the space, I don't think it would work outside in temperature below 45F. That is the
minimum temperature in the installation manual.

So is it a net game, the cool air blowing out overcoming the 3500 btu/hr the tank can deliver to the floor?
Will the slab feel warm even with the cool air blowing out?

ChrisJ

It's a damn shame.

They know how to make such systems run for decades without being touched.

I guess they would rather move product.

JakeCK

12 hours to bring up the tank to temp? Mine was able to get it up to a usable temperature on hp mode in a couple of hours when I first installed it. It is only a 50gallon compared to your 89 but still Is yours a 115v version? 

I've had mine for 2.5 months now. It can generally keep up with demand in HP mode. I've only used the electric elements a couple times when we had really high demand. Normally I have it timed to optimize usage from the PV system. Actually the schedule is where I keep having issues. I've already contacted rheem once about it. For some reason it will occasionally not follow the schedule. The first time I didnt catch it until almost 5 pm. I ran out of hot water mid shower after the wife showered herself and bathed the kids and did a load of laundry. The tank tank hadn't ran all day and was still set to off. I was very annoyed.

So far it seems to be using about 100kwh a month, increasing my electric usage by 1/6th in the cooler months. Surprisingly my PV system is damn close to still entirely offsetting my electric usage. So far for the month of December I've only pulled 12kwh from the grid. If a get a couple more days of good sun I might break even. Over all I feel swapping out my gas fired tank from 07, before failure, for a hpwh was a good call in my case. It is keeping the basement a bit chilly. Sure the uninsulated boiler pipes are losing more heat now but my server cabinet and deep freezer love it. 

hot_rod

JakeCK said:

12 hours to bring up the tank to temp? Mine was able to get it up to a usable temperature on hp mode in a couple of hours when I first installed it. It is only a 50gallon compared to your 89 but still Is yours a 115v version? 

I've had mine for 2.5 months now. It can generally keep up with demand in HP mode. I've only used the electric elements a couple times when we had really high demand. Normally I have it timed to optimize usage from the PV system. Actually the schedule is where I keep having issues. I've already contacted rheem once about it. For some reason it will occasionally not follow the schedule. The first time I didnt catch it until almost 5 pm. I ran out of hot water mid shower after the wife showered herself and bathed the kids and did a load of laundry. The tank tank hadn't ran all day and was still set to off. I was very annoyed.

So far it seems to be using about 100kwh a month, increasing my electric usage by 1/6th in the cooler months. Surprisingly my PV system is damn close to still entirely offsetting my electric usage. So far for the month of December I've only pulled 12kwh from the grid. If a get a couple more days of good sun I might break even. Over all I feel swapping out my gas fired tank from 07, before failure, for a hpwh was a good call in my case. It is keeping the basement a bit chilly. Sure the uninsulated boiler pipes are losing more heat now but my server cabinet and deep freezer love it. 

This Rheem can be locked into efficiency mode, no resistance kicks in. It is 240V drawing 1.5A when running. I saw some reviews online of 4 different brands, the GE suggested 12 hours for their 80 gallon with 68° ambient air tank to 120F, but did not indicate starting water temperature.

EdTheHeaterMan

Zman said:

I must be missing something. Is the water heater taking heat from the air in space and dumping it in the slab in the same space?
Sorry, first cup of coffee....

This sounds like a reverse perpetual motion machine. Heat the floor with a machine that is cooling the air in the same space. Using the Sun for electricity to power the machine. Can we use a groundwater open loop to make it more interesting? as the water is discharged out the ends of the radiant floor tubes, is should be collected and pumped into a water tower. the pump can be operated by a water mill at the exit of the radiant tubes.

Give me some more time and I will build an entire grid system in case Texas gets snow again this winter.

EDIT: Is it too soon to joke about the Texas snow event?

JakeCK

hot_rod said:

This Rheem can be locked into efficiency mode, no resistance kicks in. It is 240V drawing 1.5A when running. I saw some reviews online of 4 different brands, the GE suggested 12 hours for their 80 gallon with 68° ambient air tank to 120F, but did not indicate starting water temperature.

I've read mine will override the settings and actually use the elements even when set to hp only. But I have not seen that behavior yet. The few times I've needed more I manually switched it to hybrid. It'll be interesting come January. The reservoir is right across the street and is actually a large castle looking above ground tank. The water coming into the house will fall into the upper 30's.

ChrisJ

hot_rod said:

ChrisJ said:

Jamie Hall said:

Lett's see here... cranking up the calculator (there was a time I could do this holding numbers in memory. Must be getting old). That temperature rise is somewhere around 41,000 BTU. In 12 hours, works out to about 3,500 BTUh. Which, as an aside, indicates a pretty good COP -- 1.5 amps is only about 200 watts, so your getting a factor of about 5 there. Not bad.

However...

3,500 BTUh is a pretty far piece from 28,000 BTUh.

Worse, the heat pump water heater can't be in the space being heated...

It would be interesting if it was. We've seen weirder things.

It's 48 outside today and sunny giving me some solar gain, that 3500 btu/hr will cover the load today.
The heater is inside the space, I don't think it would work outside in temperature below 45F. That is the
minimum temperature in the installation manual.

So is it a net game, the cool air blowing out overcoming the 3500 btu/hr the tank can deliver to the floor?
Will the slab feel warm even with the cool air blowing out?

My guess is it'll be a huge failure.
The floor has a lot of mass, as do the things it's radiating to.

Air has very little mass. Kind of like trying to start a Cummins from a single AA battery.

The air will get cold enough the heat pump won't tolerate it anymore and the floor will still be cold.

JakeCK

Wait @hot_rod are you trying to heat the concrete floor with this? O.o 

That ain't going to work, laws of thermodynamics and conservation prohibit it. 

Maybe if it was in different room or building it might do something. 

Now I'm confused. I thought he was just trying to get dhw?

hot_rod

EdTheHeaterMan said:

I must be missing something. Is the water heater taking heat from the air in space and dumping it in the slab in the same space? Sorry, first cup of coffee....

This sounds like a reverse perpetual motion machine. Heat the floor with a machine that is cooling the air in the same space. Using the Sun for electricity to power the machine. Can we use a groundwater open loop to make it more interesting? as the water is discharged out the ends of the radiant floor tubes, is should be collected and pumped into a water tower. the pump can be operated by a water mill at the exit of the radiant tubes. Give me some more time and I will build an entire grid system in case Texas gets snow again this winter. EDIT: Is it too soon to joke about the Texas snow event?

Well put, Ed. I was going for that reverse perpetual motion concept😂

Solid_Fuel_Man

Remember that it will put out more heat than it steals from the space. The heat to cool the compressor is added to the net heat output. But then you are close to resistance electric heat. 

@ChrisJ
Yes, I'm very well aware that nothing is free. A hot boiler room can benefit from a heat stealing device, I've been in way too many 100+ degree boiler rooms where things don't last as long due to the heat. 

xjazzwreck

FYI, I use a Rheem for DHW and it's working great now that I've ducted the cold air exhaust outdoors. It still steals heat from the space but it's near the boiler and at least it's not making our basement colder.

I love the idea of trying to use these for heating, could it be retrofitted to be used as a buffer tank with a boiler that will only kick on when needed?

Solid_Fuel_Man

You can steal heat from the very space which you are trying to heat. But I think that's what Hot Rod is doing? And it's apparently working? 

JakeCK

xjazzwreck said:

FYI, I use a Rheem for DHW and it's working great now that I've ducted the cold air exhaust outdoors. It still steals heat from the space but it's near the boiler and at least it's not making our basement colder. I love the idea of trying to use these for heating, could it be retrofitted to be used as a buffer tank with a boiler that will only kick on when needed?

Wait are you exhausting the cool air from a heat pump water heater outside? Is the air it is drawing from also outside? 

If not I see several problems with that. One is that the cool air it expels is still considerably warmer than the air outside. Second where is the air that is replacing what is exhausted coming from? Outside? See the problem?

ChrisJ

JakeCK said:

Wait are you exhausting the cool air from a heat pump water heater outside? Is the air it is drawing from also outside? 

If not I see several problems with that. One is that the cool air it expels is still considerably warmer than the air outside. Second where is the air that is replacing what is exhausted coming from? Outside? See the problem?

An awful lot of people seem to be under the impression that you can blow air outside and yet not bring any air in to replace it.

Kind of like all of the forced air systems where people think only supplies matter and you can blow hot or cool air into a room and it doesn't need to return back to the blower in some manner.

hot_rod

JakeCK said:

xjazzwreck said:

FYI, I use a Rheem for DHW and it's working great now that I've ducted the cold air exhaust outdoors. It still steals heat from the space but it's near the boiler and at least it's not making our basement colder.

I love the idea of trying to use these for heating, could it be retrofitted to be used as a buffer tank with a boiler that will only kick on when needed?

Wait are you exhausting the cool air from a heat pump water heater outside? Is the air it is drawing from also outside? 

If not I see several problems with that. One is that the cool air it expels is still considerably warmer than the air outside. Second where is the air that is replacing what is exhausted coming from? Outside? See the problem?

When I first ran it the garage door was open, it was 48 outside and 48F inside, no other heat in the shop to be had. The sun was out, so at least I had some radiant heat on my body

After 8 hours I closed the shop, still at 48F and let it run up to 120F, door closed, no other heat. I wasn't in the shop when it reached setpoint 120. I assume, and based on the manual, that it took another 2 hours of so to raise from 90F after 8 hours to 120F shutdown.

Did you check the current draw on yours? I'd be curious to know what yours draws in HP mode, and if the elements ever kick in even in efficiency mode.

At this point I will use it in my house in the summer months. I'll have good PV production and could use the cooling effect in the basement.

In the shop, even if it did work it takes up a lot of space and is a bit to noisy for me.

JakeCK

hot_rod said:

When I first ran it the garage door was open, it was 48 outside and 48F inside, no other heat in the shop to be had. The sun was out, so at least I had some radiant heat on my body After 8 hours I closed the shop, still at 48F and let it run up to 120F, door closed, no other heat. I wasn't in the shop when it reached setpoint 120. I assume, and based on the manual, that it took another 2 hours of so to raise from 90F after 8 hours to 120F shutdown. Did you check the current draw on yours? I'd be curious to know what yours draws in HP mode, and if the elements ever kick in even in efficiency mode. At this point I will use it in my house in the summer months. I'll have good PV production and could use the cooling effect in the basement. In the shop, even if it did work it takes up a lot of space and is a bit to noisy for me.

I bet that 48f affected it. I don't have the tools to check its amperage. But I can guess its around 2.5 to 3 amps once the compressor is running. Drawing about 500 to 600 watts at 240v. If it kicks in the elements I will know real quick. The home automation will log it.

I can't wait to see how it does this summer. I'm hoping it makes a dent in the humidity during the day. I a dehumidifier that runs just about 24/7 for 6 months of the year and that thing actually heats the basement in to the 80's. 

Here a screen shot showing the logs and graphs from my home automation, I noted the spikes in usage:

ChrisJ

Let's not forget amperage doesn't indicate wattage when dealing with inductive loads like motors.
The VA might be close to the wattage, or it could be double the actual wattage.

JakeCK

ChrisJ said:

Let's not forget amperage doesn't indicate wattage when dealing with inductive loads like motors. The VA might be close to the wattage, or it could be double the actual wattage.

So P=V*I doesn't apply?

ChrisJ

JakeCK said:

ChrisJ said:

Let's not forget amperage doesn't indicate wattage when dealing with inductive loads like motors.
The VA might be close to the wattage, or it could be double the actual wattage.

So P=V*I doesn't apply?

On inductive loads like this, nope.

For example I have motors drawing 2.5 amps @ 120 volts but only 180 watts.

The current is out of phase from the voltage.
https://en.wikipedia.org/wiki/Power_factor

JakeCK

My guess of 3 amps at say 500watts of power probably isn't far off. Even if you doubled the amps at 600 watts your still only around 5 amps. And I would imagine rheem would have a pretty efficient compressor considering it has to share a 30 amp circuit with 2 large elements. 

PC7060

The HPWH in @hot_rod application isn’t really stealing heat but rather relocating it from the air back into the radiant slab where it can be stored until released back into space. Slab are much less sensitive to heat loss if door is opening and closing often. 

ChrisJ

PC7060 said:

The HPWH in @hot_rod application isn’t really stealing heat but rather relocating it from the air back into the radiant slab where it can be stored until related back into space. Slab are much less sensitive to heat loos if door is opening and closing often. 

Due to the little amount of energy content in air I'd disagree with that.

PC7060

ChrisJ said:

Due to the little amount of energy content in air I'd disagree with that.

Well given that's the entire premise of heat pump operations you may want to reconsider.

ChrisJ

PC7060 said:

ChrisJ said:

Due to the little amount of energy content in air I'd disagree with that.

Well given that's the entire premise of heat pump operations you may want to reconsider.

With all due respect I'm not sure how to respond.