Heat Pumps Harmonizing Heating and Cooling Needs

curiouscarbon

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Hello,

People like lower temperatures for some times, and higher temperatures for other times. It seems to need a lot of electricity energy..

Heat pumps, especially in the form of refrigerant based compressor systems, and also peltier based systems, are capable of controlling heat flow with electricity.

By considering and harmonizing all the heating and cooling needs of a local system with all the available heating and cooling sources, it should be possible to enjoy both more reliably with even less energy use than historically common methods.

Arduino helps many creative experimenters measure temperature and switch DC coolant pump every day :) why not measure temperature of multiple places on RV or home or other place, and then have a small computer automatically harvest heat from whichever sources are providing the most at that time and feed that to a heat pump?

Please help me fill in this graph..

1628590447593.png

One incarnation of the idea is that if the air is warm and it's sunny, the panels are probably quite warm too. Use a heat pump to move heat from backside of photovoltaic panels and from air, to serve water heater BTUs.

Or, if it's cold outside, supplement heat coming from the air with heat from the backside of the panels.

Of course it's a bad idea to pump endless amounts of heat into a photovoltaic panel, but it's safe to pump heat back into them if the temperature stays below whatever safe range that minimizes PV production loss. This would happen on a just slightly too warm evening. Pump a small amount of heat into the back of the panels at night to cool the inside air. The breeze would whisk that heat away easily from roof mounted solar panels.

Does anyone currently use their solar panels as water source heat pump? What is the performance like? How are cloudy days?

What sort of interesting circuits of heat can you imagine that haven't already been realized in practice?
 

Supervstech

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Interesting.
I guess, you are visualizing a water source heat pump, and redirecting the discharge heat to places that are cool? The water heater idea is often built into most water source heat pumps… usually there is a loop connection for heating a tank of water… or feeding a special h2o tank loop… the issue of heating a PV panel… unlikely to ever have low PV temp when excess heat is in the loop… possible, but unlikely…
 

curiouscarbon

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Without having a specific application/situation in context, discussing it can be hard maybe.

e.g. Lately there have been some threads about water heating from "solar" and that is one big application to harness this approach for on my compass. Indeed start with multiple-heat-source water source heat pump and work from there is the idea. Most use air as heat source from what I see on this forum. A few mention ground. Some floating folks mention water.

Example application context: "it's cold outside" -> heating. heat up tank of water. heat of body of air. heat up person.​

But where to source this heat? People on this forum seem to live in all sorts of different conditions. What is possible depends on Local Conditions heavily. Rain often?, Vehicle or building? Often cloudy? Windy often? Snowy often? Dry often? Insulated? Need hot water or not? Need cooling or not? Want on demand or ok with wait?

Trying to approach from a perspective that could easily address edge case needs in weird climates readily based on needs input into the arduino program. e.g. connect water source heat pump, two or three sources of heat, each with thermometer and individual water/coolant loop that can selectively circulate with the main buffer tank. User input would be "i want tank A kept at 50°C and i have air source heat and solar thermal source heat" and the microcontroller would selectively circulate water/coolant in the air or solar thermal loops to provide the water source heat pump with heat to do the task. probably at solar noon the solar thermal heat source circulation pump would run the most. at night, the air source circulation pump would run the most. water based radiators have different performance tradeoffs vs refrigerant based radiators.

A normal photovoltaic solar panel will act as a simple solar thermal collector as a matter of course. I'm curious how feasible it is to harvest this low grade heat for water heating for tank for shower or hydronic or air heating.
 

curiouscarbon

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Here's two situations that are related but subtly different: only needing to heat water, vs needing to heat water and the air in a space.

1628596316529.png

Stacked plate heat exchangers would be a useful tool in facilitating some of these situations, I think..
 

curiouscarbon

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unlikely to ever have low PV temp when excess heat is in the loop… possible, but unlikely…
I agree that it's unlikely! Still, I would like to experiment with a system that is sensitive and flexible enough to notice a confluence of conditions and act to meet the stated goal.

Someone sleeping in a van, in a desert, where it's 28°C and 40% relative humidity outside with a slight breeze going wants to cool off.

Surely since it's nighttime, and there's no solar production to spoil with negative voltage temperature coefficient dance, it's perfectly fine to push their temperature up to at least 50°C, maybe even 60°C or 70°C depending on comfort level. That represents BTUs not dissipated by a cross breeze that could have otherwise helped cool someone sleeping in a van... or something.

I hope this makes some sort of sense.

Probably not a good idea to install sideways blowing fans on the roof to move air across the solar panels to increase the heat dissipation, that could add dust or waste energy or cast a shadow on the array.
 

curiouscarbon

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I guess, you are visualizing a water source heat pump,
Most users of this forum would agree that refrigerant based compressors are very good option with lots of proven track record.

Warning, might want to vacate coffee from your mouth prophylactically🤣

For now I’m using solid state heat pump because it’s fun, and dealing with refrigerant in a small area is annoying to DIY. This is what the water source heat pump looks like for my current iteration:
1628598104297.png

It’s 2x2 geometry of 40x40mm TEC1-12715 modules stacked ten layers high, between two 80x80mm aluminum water blocks, with thermal pads between each mutual face.

I intend to wire each column of ten modules to be wired in consecutive series. This will yield four strings. 10S4P wiring. Driven with a 3S LiFePO4 battery pack, each peltier plate will receive 0.9~1.02 V under normal operation. Please do note that this drive voltage is noticeably lower than the drive voltage selected by most people talking about peltiers :giggle: looking forward to testing this with my custom arduino firmware.
 

curiouscarbon

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found this example of people testing this type of harmonized multi-heat source approach

Experimental study on the operating characteristics of a novel photovoltaic/thermal integrated dual-source heat pump water heating system​

Highlights:
•We propose a solar PV/T integrated dual-source heat pump (DSHP) water heater
•The system works efficiently in both water–water mode and air–water mode.
•We suggest the system adopting air–water mode when solar energy is insufficient.
•In Shanghai, the electrical conversion efficiency can be increased by 10.3%.
The results showed that when water side evaporator was used, the PV/T panel operating temperature can be decreased up to 45 °C, and the electrical conversion efficiency yielded a surplus of 10.3%.

1628601009028.png
 

curiouscarbon

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Numerical Study of Integrated Solar PhotovoltaicThermal Module with a Refrigeration System for Air-Conditioning and Hot Water Production under the Tropical Climate Conditions of Singapore​


Proposed System
The proposed PVTR system produces electricity, hot water and air-conditioning at the same time by integrating solar PVT and VCR systems. Electricity is produced by the PV cells, while the refrigeration system produces hot water at its condenser and air-conditioning (cooling) at a section of the evaporator through a fan coil unit (FCU). At the same time, the refrigeration system also cools the PVT modules to optimize their performance
In this study, a novel integrated solar photovoltaic–thermal–refrigeration (PVTR) system used to produce hot water and air-conditioning in the tropical climate conditions of Singapore was analyzed.
The results show that attractive electrical and thermal perfor- mance can be achieved with a maximum annual cooling COP of 9.8 and a heating COP of 11.3. The PV e±ciency and power saving were 14% and 53%, respectively.
More recently, however, PVT modules coupled with refrigeration system have been gaining attention too. Here, the compressor is powered by the PV panel while thee PVT module itself also serves as the evaporator of the refrigeration system. The evaporator cooling effect lowers the solar cell working temperature and improves the PV efficiency. This arrangement can give an even better performance as compared to air or water cooled systems.
1628602773436.png

What do you all think?

Cool down the solar panel and increase yield, while simultaneously performing useful heating and cooling.
 

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toms

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Looking forward to following your adventures with this - “cool” project.
 

Bob B

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I love outside the box type thinking .... very interested in what you come up with.
 

sunshine

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Hello,

People like lower temperatures for some times, and higher temperatures for other times. It seems to need a lot of electricity energy..

Heat pumps, especially in the form of refrigerant based compressor systems, and also peltier based systems, are capable of controlling heat flow with electricity.

By considering and harmonizing all the heating and cooling needs of a local system with all the available heating and cooling sources, it should be possible to enjoy both more reliably with even less energy use than historically common methods.
Giant water battery helps university cut energy costs by 40 per cent

Limiting factors at home is the initial cost of heat pumps and the on going maintenance required as in anything with moving parts.

"
Cool down the solar panel and increase yield, while simultaneously performing useful heating and cooling."

I do have 2sq meters of poly pipe under glass directly facing the sun, Have thought about a similar setup below the panels as you have suggested. However a stand alone setup is more cost effective.
 
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svetz

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... it's safe to pump heat back into them [solar panels] if the temperature stays below whatever safe range that minimizes PV production loss. This would happen on a just slightly too warm evening. Pump a small amount of heat into the back of the panels at night to cool the inside air. The breeze would whisk that heat away easily from roof mounted solar panels.
AFAIK, there is no temperature too low for panels. Although using them as radiators at night is possible. Since ΔT drives heat flow, there would have to be a fair temperature difference for economics. If ΔT was big, then you'd want to keep the heat inside the house and it wouldn't be needed. if ΔT was small, economics might favor opening the windows and letting the warm air out rather than a heat exchanger system.

Without having a specific application/situation in context, discussing it can be hard maybe.
Impossible I'd say. Heat pumps or recapturing small ΔT changes as energy work, but if they're warranted or not depends on the economics. For example, boosting power with sterling engines might work on offshore solar farms as the panel temperature might be 130° and the water temperature 70°. But on a normal roof, unless engineered for it, you might only get a ΔT of 10°.

e.g. Lately there have been some threads about water heating from "solar" and that is one big application to harness this approach for on my compass.
This might make sense, but it's a lot of additional plumbing to go wrong later, and anyplace it gets cold needs an antifreeze system with a heat-exchanger and pumps that drive costs up.

Let's say a hot water tank consumes 10 kWh/d, here that's $1.30 per day (soon to go up) or $475/yr. So, such a system would need to be under $5000 and maintenance-free for a decade. At $.50/W, PV panels meet that energy need and are under the price point.

So, from my thinking it's not can it be done. It's should it be done?
 
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curiouscarbon

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I’ll be starting at the very small scale first to prevent any economic catastrophe 😃

My “small goalpost” for now is to set up a system capable of pumping 100W at CoP of at least 2, from a solar panel in back yard, into an insulated bucket of water. 5 gallons of water can buffer 80,000 W for one second with 1C increase. Log temperature of panel, coolant, bucket, ambient air..

Just a single 100-150W panel, with some hacked tubes on the back, maybe snake copper along the back with thermal pads.. silicone isn’t conductive enough.

It’s funny, I’ve started thinking of some of the negatives as positives in some way. Being able to unscrew and replace the pump without having to think about evacuating the tubes is nice. But removing air bubbles isn’t. C’est la vie.

I think water based is good for hobby experiments like my current scale. Maybe it won’t scale up :)

Thank you for the feedback, it helps me guide my experiments more productively🙏
 

pinkeng

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I actually look at this about 20 years ago when a 100 watt solar panel was about $800. In theory you can extract heat from the back of a solar panel. Let's say you want to extract 110 degree water and stored in a small hot water tank. Problem with this is that your solar panel needs to be at 120 degrees because there's always an approach temperature to transfer the heat from one side to the other. The tubing on the back of the panel will reduce panel heat loss causing the panel voltage to drop.

for maximum PV generation you want the panels as cool as possible. As a preheater it works really well. say heating water from 50 degrees to 70 degrees. Then the PV panel stays cool and life is pretty good. This might actually work for a hydronic heating water source heat pump. Provided you have enough panels as you need low grade water temperature say around 60° to heat the house and extract hot water to a hot water heater. Trying to get hot water Direct from the back of a PV panel say in the order of 120 to 130 degrees will greatly degrade the the voltage output thereby affecting the entire solar wattage output.
 

pinkeng

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Using refrigerant say from a compressor will not lower the PV panel temperature. You use the condenser located on the outside ac unit which generally has the compressor to drop the liquid refrigerant temperature about 10 degrees. Because the refrigerant has been compressed it's actually hot. The condenser rejects that heat from the refrigerant to the outside air. You only get cool temperatures after the refrigerant expands at the evaporator coil inside the refrigerator or your A coil on your indoor fan coil unit.

My back-of-the-napkin calculations says you would heat 5 gallons of water 8 degrees an hour using the back of a hundred watt solar panel. You'll get roughly 341 BTUs out of the 100 Watts of energy extracted off the back of the solar panel. That's probably a fairly good number since the back of the panel is a non-conductive plastic which is not the best heat transfer medium. there have been several companies that were experimenting with that idea but I don't think it ever got off the ground. Using solar panels with a water source heat pump might actually work because it's fairly low quality Heat. But you're going to need a lot of panels. From heating hot water standpoint it's better to use a solar hot water panel that's design for the high delta T throughput.
 
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