Warm water heat pump 5kwh/day

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Pepe

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Jun 20, 2021
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Today the warm water heatpump runs with night electricity, about 10ct/kwh. Day tariff is 20ct/kwh. Heats up a 300 liter tank to 55 deg C.
I can program the pump to turn on and off at a certain time, but i can not remote control it.
The pump absolutely doesent like brown-outs or to be switched on/off.
Consumption is 500W, run time max 10h / day.

What are my options?
 

OffGridInTheCity

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Today the warm water heatpump runs with night electricity, about 10ct/kwh. Day tariff is 20ct/kwh. Heats up a 300 liter tank to 55 deg C.
I can program the pump to turn on and off at a certain time, but i can not remote control it.
The simplest would be to program it to run/heat-water at night (10ct/kwh). Or do as much as possible at night so you can make it thru the day with it off. Would that give you enough hot water for the day time?

Consumption is 500W, run time max 10h / day.
A next level would be to have a battery system that charges using 10ct/kwh power and then runs the pump thru the day. 12hrs * 500w = 6kwh of useable battery capacity. So you need a 8 or 10kwh battery with charge/inverter and ups.

Another 'next level' would be to increase the size of the hot water tank so it can supply hot water thru the day without needing to be heated until the following night. Maybe add a 2nd tank?


The pump absolutely doesent like brown-outs or to be switched on/off.
I have Rheemes heat-pump hot water tank - and its OK with ATS (split second) switchovers between grid and inverter / a UPS is not needed and this might be true for yours as well. But in worst case - a 500w UPS unit is not that hard to find.
 

prepared1

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Jan 17, 2021
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Pepe: Do I understand your pump wattage correctly? 500 watts? Are you running a high head pump? I'm running 8-12 zone Wirsbso manifolds with Grundfos Alpha pumps, and my average consumption is 11-18 watts each. This is for in-floor and radiators both.

If your pump is old, swap it out and get a quick payback on electrical savings. Taco has good versions, and so does B&G.

Good luck.
 

prepared1

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Jan 17, 2021
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Pepe: I misunderstood. Got it. Before I made any significant changes to your system I'd make sure that you have done everything possible to reduce heat loss. Extra insulation for the tank, careful insulation of piping. If you have PV, you might consider installing a drain-back solar panel, and using your existing tank. I'm doing that right now. My intent is to get a dc pump to run during the day straight off a PV panel. At night, when the temp drops, the system shuts off anyway, and drains back to the tank. All of that expense would count for Federal tax credits. I don't know your location, however.

I've done some flip-flopping lately on the logic of how much to spend on any particular utility. Changes in technology make it possible to rethink your plans. In general, I don't expect natural gas to stay at current low levels though. Ours just went up 13% due to the Texas fiasco.

Just a thought.
 

Pepe

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Jun 20, 2021
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> drain-back solar panel,
Way too much work.

I do search a way to use solarpanels and a grid-tie to run that heatpump.
Problem is on cloudy days i want the pump to run in the night for 10ct/kwh and on sunny days during the day. I coud probably misuse local weather forecast to plan this. But the heatpump has no remote control, just a timer. I think batteries would be simple but way to expensive.

I got 3kw of solar panels, got them for 50ct/Watt, not yet mounted, 3 of the 10 in the garden for testing.
 

not2bme

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Oct 16, 2017
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You should give some more details about your system, rather than let us speculate what you have.

You don't mention what the hot water heater is used for. If it is for residential then the heat pump only kicks on during the mornings and nights when people are at home using it. So most of the time it is almost idle. If it's for heating some process application, like a vat of lard, then it is a different story.

You also want something that switches between grid and solar, so this is not a direct pv application. I'm assuming that you said it costs you money running from the grid, so I'm thinking this is not a DC application as well. You want to run on utility during the nights and pv during the day when there's solar. Now for that you need an inverter that can switch between grid and solar. Mppsolar makes some really affordable units that run on grid and solar, and some have batteryless operations. For a low wattage under 2kw they can be had for around $500-600. That way it doesn't cut out if it is a rainy day or at night but instead run from the grid. During a rainy day, a 3kw solar array will produce a whopping 100w. The only thing it doesn't do is prevent you from running it from grid during the day instead of just shutting off (let's say it does switch over to grid because it is rainy). Then you can later think about hooking up some batteries just to smoothen the load especially when you use it only during peak times (mornings and nights).
 

prepared1

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Hey OGITC: Could you detail a bit on how you are using your ATS? I know I've read some stuff about it, but when I do a search, so far I have not found the posts. I don't want to hijack PEPEs post though.

I'm interested in how an ATS can be used basically off grid in the city, just like your name.

Thanks!
 

OffGridInTheCity

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Hey OGITC: Could you detail a bit on how you are using your ATS? I know I've read some stuff about it, but when I do a search, so far I have not found the posts. I don't want to hijack PEPEs post though.

I'm interested in how an ATS can be used basically off grid in the city, just like your name.

Thanks!
Sure. Its a "Y". You wire in grid and wire in solar-inverter and then the output will switch back and forth between the 2.

Some all-in-one units do this + have UPS- for example my MPP Solar 3048LV in the trailer does this. In my home system, I have individual components instead of the more 'modern' all-in-one units - so the following is in that context.

To install these things you need to have
1) Incoming grid power
2) Incoming inverter power
3) Outgoing to the load.

Here's a 240v@50a "Progressive" ATS example at my main panel it was easy to hook up incoming grid power but I had to run 150ft from the inverter for the incoming "Inverter Power" circuit. The output goes to the MTS above - but that was just a way to feed the output into the main panel circuits so I could flip a switch to control individual circuits. One could wire the output directly to the panel.
1629054404179.png


Here's another 240v@50a example with a "Progressive" ATS placed under the house right near the external (condenser) portion of the whole-house heat-pump.
1) Incoming grid is the 'grey' wire. This is the original wire to the heat-pump condenser that I just pulled it thru the wall from the external on/off box outside.
2) Incoming inverter is the 'black' wire - had to run it from the inverter on the other side of the house. The extra black wire is where I 'continued' it over to another ATS.
3) Output goes back out to the external on/off box to power the condenser.
1629054507765.png


Here's a pair of 120v@30a examples of the "Go-Power" (boxs with yellow) ATSs that power the APC UPSs.
1629055292463.png



In all these cases, when the inverter (e.g. solar system) is off, grid runs thru the box to the output just as it always has. When the incoming inverter circuits are energized, the ATS will 'notice it' and auto-switch over to the incoming inverter power. When the inverter shut-off, it automatically switches back to the (default) grid power.

Suggest going to @daromer's channel and search ATS - he did several youtubes such as the one below. The only difference in my implementation is that I bought commercial UL/ETL listed units with 30sec delay control boards instead of constructing them myself.
View: https://youtu.be/KJ3_OyOl06Y
 
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Pepe

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You should give some more details about your system

Its for residiential warm water. Heats up 300L in an isolated tank. Water will be used during day and replaced with cold water, temp will drop substantially. Runs during 10ct/kwh low energy cost periods at night, 500W continuous, 2kw startup. I can program it to reheat but i prefer not to.

I have never considered ATS. I didnt know about it. Have to read up about it, your info is quite dense for an old man.
I thought about a grid-tie inverter. There are cheapo ones from china which seem to work nicely.
I do not consider a battery any more since i would need a 5kwh one which ist quite expensive.

I found out the issues is swiching on the heat-pump remotely when there is enough power from the sun. Then at night start it again until it reaches set temperature and switches off. Writing posts and reading the answers did clear the fog in my brain. TY for that.

You have a "whole house" heatpump? My dream :)
 
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not2bme

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Oct 16, 2017
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Its for residiential warm water. Heats up 300L in an isolated tank. Water will be used during day and replaced with cold water, temp will drop substantially. Runs during 10ct/kwh low energy cost periods at night, 500W continuous, 2kw startup. I can program it to reheat but i prefer not to.

I have never considered ATS. I didnt know about it. Have to read up about it, your info is quite dense for an old man.
I thought about a grid-tie inverter. There are cheapo ones from china which seem to work nicely.
I do not consider a battery any more since i would need a 5kwh one which ist quite expensive.

I found out the issues is swiching on the heat-pump remotely when there is enough power from the sun. Then at night start it again until it reaches set temperature and switches off. Writing posts and reading the answers did clear the fog in my brain. TY for that.

You have a "whole house" heatpump? My dream :)

Grid-tie is an option, but to properly do it would cost a lot and to get the right permits for your local electrical codes. Yes you can do it the cheap chinese grid-tie option, illegal but still possible.

Without batteries, your options are limited getting your heat pump to work when needed. Like I mentioned before you can try a mppsolar unit. But it doesn't prevent switching to grid when it goes cloudy during the day. If you're handy with programming and you can remotely control the heat pump water heater then you can put toether some controller that detects if it is running on grid or solar.

Have you tried thinking out of the box? Have another water heater, but runs on electric? You can install a pre-heater that's just another water heater before your heat pump water heater. Then just directly power the heating element directly from your solar panels. THere's no controller other than a temperature cutoff.

View: https://www.youtube.com/watch?v=BSSQ6IRve4Y
 

floydR

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Aug 23, 2017
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look at this thread I believe Cheap 4-Life found a solution that works for him, might work for you but I think you would need a battery bank.
Later floyd
 

Pepe

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Have another water heater, but runs on electric?

My heat-pump has an additional resistive heating element built in. I could abuse that for solar.
I could use it to burn off the excess solar production. Nice and simple idea.

I wonder what is the best way to control the power output of a resistive heater. Must be linear and smooth.
If it was DC i would abuse an adjustable buck converter, but it's AC and 240V.

My actual limiter uses orangepi and RS485 for in-output, done in python.
 
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not2bme

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Watch that video in my post. What he has is a hot water heater with two heating elements (usually a top and bottom). He left the one element alone on AC and hijacked the other to run on direct PV. There's also no such thing as a AC or DC element (or not any that I'm aware of). They run on both AC or DC. The only thing is that you have to match the power or you only get a quarter of the rated output. So for example a 240V 4000W element will only produce about 1000W at 120V. There's another youtube video on how to calculate that.

There's no need to have any linear or smooth power. Just full on and off is fine and easy to use. Usually you would just look for a relay to turn it on and off, with a temperature probe. But it's hard to find a DC relay that works on high voltage and amps. I actually found a solid state relay that works up to 100V at 30A.

THe youtuber actually has an update with what I'm talking about.
View: https://www.youtube.com/watch?v=2nEfElD7B5s
 

Pepe

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Are there corrosion problems using a heating element designed for AC?

You did misunderstand the "smooth power" thing. My setup is "not inspected", basically illegal, i am not allowed to feed power to the net. I use a "limiter grid-tie inverter" which produces only the power my house needs. I have an RS485 meter in the basement which tells the grid-tie inverter how much power to maximally make. I love grid-tie since it mixes solar and grid power seamlessly.

If solar makes 900W and house uses 100W i want the heater to take exactly 800W. Not sure how to do it, a remote control variac would be ideal but way to expensive.

Is that you in the video? Clever way to adjust summer-winter angle!
 

not2bme

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If you already have a grid-tie, then run the device on AC. You will find a hard time trying to balance power like that. Reason is you don't know what your max PV output is at any time without actually outputting that power. Or find a commercially available product.

hbpowerwall installed a device that does this. Maybe you can figure out their logic. Not sure the youtube link but search for it. https://myenergi.com/product/eddi
 
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