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mackey
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join:2007-08-20

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Re: [Green Tech] Solar assisted heat pump, anyone know something about these??

said by robbin:

If you use a compressor to reach a certain pressure and temperature, how is that different than heating the gas to reach a certain temperature and pressure.

You are assuming the temperature and pressure will be the same in both cases. They will not. When a gas is compressed and heated as a side effect of that compression the temperature will be MUCH, MUCH lower then if that pressure were to be reached by heating alone.

/M
iknow_t
join:2012-05-03

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said by robbin:

The system and refrigerant aren't designed for lower pressure. In fact, the newer ones are much higher pressure than the old ones.

Ground source heat pumps are an entirely different topic. We are not talking about the medium of the heat exchange but a part of the refrigeration process.

the system and refrigerant are designed for the pressure that normally occurs with a compressor, raising the temperature of the gas going into the condensor makes it above normal. and yes, the part of the refrigeration process that makes ground source heat pumps in cooling mode more efficient is relevant, since the effect of cooling the gas more makes it more efficient. it's not the medium, it's the cooling effect that matters.

robbin
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join:2000-09-21
Leander, TX

robbin to Corehhi

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Found this which somewhat explains what they are trying to do

" In a traditional DX air conditioning system, the compressor is sized to produce the required refrigerant pressure at the expansion valve, as well as the temperature differential at the condenser for efficient heat rejection. This results in a compressor
which is capable of pressures larger than required. In the Sedna Aire Solar AC unit, the compressor is sized solely on the pressure requirement, with additional heat input for condenser heat rejection being provided for much of the time by solar vacuum tube collectors. This allows the use of a modified compressor, with consequent savings of around 30-50% of electrical energy as compared to a conventional system of the same cooling capacity."

»www.edwardmarcsphilinc.c ··· comfort/

mackey
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join:2007-08-20

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Re: [Green Tech] Re: Solar assisted heat pump, anyone know something about these??

said by robbin:

Here is the important part of how this could work. Referring to the video it is mentioned that the compressed refrigerant after first stage compression is about 180 degrees and their device will raise that to the equivalent of second stage 200 degrees

But the temperature rise caused by the 2nd stage compressor is only a side effect of significantly increasing the pressure. It's the pressure and flow increases which allows the 2-stage system to move more heat, not the higher temperature. Merely heating the 180 degree gas to 200 will not do much of anything to the pressure or flow and the little pressure it does add will do nothing but cause the compressor to work harder and reduce flow.
said by robbin:

Now remember that this works better the hotter it gets so we are going to assume an outside temp of 100 degrees as a for instance. The heated, compressed gas is next gong through the condenser where the 100 degree air has to cool it into a liquid state. It seems reasonable that 100 degree air can cool 200 degree gas more efficiently than it can 180 degree gas as there is a greater temperature differential.

Like was mentioned earlier in this thread, the hotter temperature does increase transfer efficiency, but the total system efficiency is significantly harmed as the condenser now has to remove the additional heat added by this device in addition to the heat from the space to be cooled. The extra heat added causes the liquid temperature leaving the condenser to be much warmer which means it can remove less heat from the space to be cooled.

/M

robbin
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join:2000-09-21
Leander, TX

robbin

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Seems very hard to find any first hand knowledge on the product. I did find this thread and it seems that too much head pressure is a problem.

»hvac-talk.com/vbb/showth ··· sted-A-C

Interesting that there are really no reviews or feedback either positive or negative.
robbin

robbin

Mod

European Installation instructions document

»www.sednaaireeurope.com/ ··· cool.pdf

cowboyro
Premium Member
join:2000-10-11
CT

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said by robbin:

Wait -- isn't the purpose of the compressor to not only increase pressure of the gas but also to raise it's temperature?

No, the purpose of the compressor is to increase the pressure. The temperature increase is a result of increasing the pressure - and the hot refrigerant can release heat outside.
Automate
join:2001-06-26
Atlanta, GA

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Re: [Green Tech] Solar assisted heat pump, anyone know something about these??

It's a scam to allow the customer to get a tax break due to the solar component. EPA/IRS needs to shut them down.
Automate

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Look at their diagram. They are saying they heat the refrigerant so they get more cooling out of the condenser, WTF. Any solar heat gain will lower the overall cooling not increase it.

But, due to the compressed refrigerant already being at a high temperature they are not going to gain much heat from the solar. When the "solarpanel" is not gaining heat from the sun it will actually increase efficiency since it will serve as an extra condenser to release heat.
iknow_t
join:2012-05-03

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said by Automate:

It's a scam to allow the customer to get a tax break due to the solar component. EPA/IRS needs to shut them down.

yes, but they never gave technical information beyond what is very vague, so they can say you got what was described!.
public
join:2002-01-19
Santa Clara, CA

public

Member

The amount of ignorance in this thread is amazing.
Before posting nonsense, why don't you simply calculate the work done by the compressor
to move 1 mole of cool gas to the high pressure side, where the pressure is elevated by the heater,
and compare to the work without it.
For simplicity assume ideal monoatomic gas.
Then recall that the condenser is not used to cool the gas, but to condense it.
jeb9876
join:2010-03-28
Morrisville, PA

jeb9876

Member

Speaking of "ignorance" and "posting nonsense" - "Then recall that the condenser is not used to cool the gas, but to condense it."

Can't get worse than that.

How do you think that heat is moved from inside a building to outside?
What do you think all that copper/aluminum fin in the condenser is used for?
It is a heat exchanger used to cool the gas and thus condense it.
public
join:2002-01-19
Santa Clara, CA

public

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said by jeb9876:

What do you think all that copper/aluminum fin in the condenser is used for?
It is a heat exchanger used to cool the gas and thus condense it.

Er... The gas is condensed by removing the latent heat, not by cooling.
Temperature does not change during condensation.

Is it the water in Pennsylvania???
Mr Matt
join:2008-01-29
Eustis, FL

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said by Corehhi:

Any one have one of these systems or know much about them???

I don't know if they are still available but I saw advertised a solar assisted Air Conditioner with a solar cell panel to provide power to reduce the electrical load.

I owned a home that had a Desuperheater, a heat exchanger and thermostatically controlled circulating pump connected to the hot water heater and hot gas outlet of the compressor. It provided hot water when the AC was running. The most efficient Desuperheaters are those built into the condenser cabinet.

cowboyro
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join:2000-10-11
CT

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said by public:

Er... The gas is condensed by removing the latent heat, not by cooling.
Temperature does not change during condensation.

However the temperature changes before and after the condensation. The refrigerant enters the coil at a very high temperature and exits ideally at the air temperature.
contsole
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join:2003-12-30
Newington, CT

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Solar assisted heat pump, anyone know something about these??

It would work so much better if those roof top coils were in the shade instead of the sun but I guess then you couldn't call it solar.
public
join:2002-01-19
Santa Clara, CA

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Re: [Green Tech] Solar assisted heat pump, anyone know something about these??

said by cowboyro:

However the temperature changes before and after the condensation. The refrigerant enters the coil at a very high temperature and exits ideally at the air temperature.

No. Most of the temperature drop occurs in the expansion valve.
Most of the heat is transferred by evaporation/condensation.
Expand your moderator at work
iknow_t
join:2012-05-03

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Re: [Green Tech] Solar assisted heat pump, anyone know something about these??

said by cowboyro:

said by public:

Er... The gas is condensed by removing the latent heat, not by cooling.
Temperature does not change during condensation.

However the temperature changes before and after the condensation. The refrigerant enters the coil at a very high temperature and exits ideally at the air temperature.

+1 public needs to read up on the refrigeration process!.
Expand your moderator at work

Sly
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join:2004-02-20
Tennessee

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Re: [Green Tech] Solar assisted heat pump, anyone know something about these??

said by public:

said by cowboyro:

However the temperature changes before and after the condensation. The refrigerant enters the coil at a very high temperature and exits ideally at the air temperature.

No. Most of the temperature drop occurs in the expansion valve.
Most of the heat is transferred by evaporation/condensation.

Are you talking just for the sake of being argumentative? He's not even talking about an evaporator. He's talking about cooling superheated refrigerant.

Temperature change "in" the expansion valve? In the expansion valve is subcooled fluid undergoing a pressure drop as it exits the valve and enters the low pressure evaporator. In the evaporator is a temperature drop. I could explain why, but you'd probably argue with that too.
scross
join:2002-09-13
USA

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OK, folks, I haven't read the patent yet (I will when I get the time), but on the surface of it the physics here (at least the "solar" aspect of it) just doesn't work! The basic purpose of the condenser is to REMOVE heat from the refrigerant, NOT to add it. The condenser does this by compressing the refrigerant gas, which causes it to get hot (this is heat LEAVING the gas) and ultimately to cool off enough to turn it back into a liquid at the operating pressure of the system. Any heat added during this process makes things worse, not better; this includes heat added by the compressor itself as a consequence of all the work it is doing.

There are improved condenser systems out there now which DO work as advertised, but they're not solar-related, and I don't know if these have worked their way down into the consumer market yet. The simplest of these that I've seen involves wrapping the condenser with external filters, then keeping these filters wet. The swamp-cooling effect from the wet filters dramatically decreases the air temperature and cooling load on the condenser, which in turn dramatically decreases the electricity bill. Your water usage (and bill) goes up, though, which would be a problem in areas where water is in relatively short supply.
public
join:2002-01-19
Santa Clara, CA

public

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said by scross:

the condenser is to REMOVE heat from the refrigerant, NOT to add it. The condenser does this by compressing the refrigerant gas, which causes it to get hot (this is heat LEAVING the gas) and ultimately to cool off enough to turn it back into a liquid at the operating pressure of the system. Any heat added during this process makes things worse, not better

Do the suggested calculation assuming ideal compressor, and ideal monoatomic gas.
Next review latent heat of condensation.
Mr Matt
join:2008-01-29
Eustis, FL

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said by scross:

The swamp-cooling effect from the wet filters dramatically decreases the air temperature and cooling load on the condenser, which in turn dramatically decreases the electricity bill.

The Desuperheater provides the same reduction of refrigerant temperature before reaching the condenser coil as the filters. I had to add an indicator light and switch to the Desuperheater to disable it when a technician was servicing the system. With the hot water circulating pump running, the refrigerant high pressure reading was abnormally low. The Desuperheater contained a 135 degree non adjustable thermostat which shut the pump off when the water temperature from the water heater reached 135 degrees. The thermostat in the water heater was set at 125 degrees. I could tell when the AC was not running, in the winter, because the hot water was noticeably cooler.

Sly
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join:2004-02-20
Tennessee

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Actually I could see a way that it could work. As the hot refrigerant vapor leaves the compressor, it then goes to the solar panels to pick up more heat. This effectively superheats the gas even more. Essentially the gas will pick up more heat and raise the pressure further.

Now with higher pressure and more heat, the gas enters the condenser. This heat is given off by the condenser to the atmosphere. But since you have an open system from the solar panels to the condenser, the pressure doesn't decrease, only the temperature. In other words the condenser cools the gas, no matter the temperature, back down to ambient. However with the solar panels, this condensed liquid is at a higher pressure. What this means is that the subcooling increases.

It's like this... Without the solar panels, hot gas leaves the compressor, cools back down to ambient in the condenser and returns to a liquid state for travel back to the expansion valve. It might take the refrigerant from 225 psi at 180º F to 225 psi ~ambient.

Now with the solar panels your temperatures and pressures entering the condenser might be 235 psi and 200º F (made up numbers). The condenser cools it to ambient but now at a higher pressure. If you have 2 liquids at the same temperature but one liquid is at a higher pressure, the liquid at the higher pressure will be subcooled more. Both liquids are at the same temperature leaving the condenser, but the one with the solar panel will be at a higher pressure meaning the subcooling will be greater and the amount of heat that can be picked up in the evaporator will be greater. This is because with increased subcooling, it will take more heat in the evaporator to raise the liquid to boiling point. Your evaporator will run colder.

What people are focusing on is the increased heat in the condenser. But assuming you have enough air flow, you are still going to cool the refrigerant down close to outdoor ambient with or without the solar panels. Yes the condenser will have more heat to give off with the solar panels, but it's not that big of a deal to remove it. What really happens is that with the increased pressure that comes as a result of the heating, you get increased subcooling once this liquid is cooled to ambient and leaves the condenser. Like I said, the liquid can now absorb more heat in the evaporator before becoming a gas. Once a liquid boils to a gas, it can no longer absorb heat. So with increased subcooling (due to the higher pressure), your liquid can absorb more heat before it finally becomes vapor.

Corehhi
join:2002-01-28
Bluffton, SC

Corehhi

Member

I need to find a real world install of this "solar assisted" system.

Doesn't look like much can be agreed on.

Sly
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join:2004-02-20
Tennessee

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I have a desuperheater and I love it. Same thing... you can really tell when the heat pump is not running. I bypassed the desuperheater's thermostat and instead run off a differential controller. This way the desuperheater pump runs any time the refrigerant is 20 degrees above the water temperature. I run mine in heating as well as cooling. Even though it will make the heat pump run longer in the winter time, it's still operating at a COP of greater than 1 so it will heat more efficiently than the electric water heater. In order to get this to work, I hooked the desuperheater pump up to the fan relay on the outside unit. This way whenever the heat pump kicks in to defrost the coils and the outside fan stops, the inside water pump stops as well so that the refrigerant can get hot enough to melt the ice off the coils.

The desuperheater does exactly the opposite of what the solar panels are doing. It drops the temperature and pressure of the high side before the refrigerant goes to the condenser. By running at lower head pressures, the compressor sees less load and uses less electricity. The heat gained by the desuperheater is free, going to my preheat water tank.

One thing I'm not sure of with the solar panels, if they heat the gas leaving the compressor, thus raising the pressure, it will also increase the head pressure which will put more load on the compressor. If the compressor is running at a higher load it will draw more current. Maybe the increased subcooling offsets this...

I eventually ended up putting a head pressure control on my system with the desuperheater. We can get cool nights and with the AC running, I was worried about liquid floodback to the compressor. It raises the head pressure by slowing down the outdoor fan, but with the reduced speed comes less power usage. The increased head pressure raises amp draw to the compressor but the reduced fan speed offsets it. Sometimes the desuperheater works so well that the outdoor fan will take several minutes to turn on and when it does it barely turns. That's saving 300 watts right there by not running the fan...
Automate
join:2001-06-26
Atlanta, GA

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said by Sly:

As the hot refrigerant vapor leaves the compressor, it then goes to the solar panels to pick up more heat. This effectively superheats the gas even more. Essentially the gas will pick up more heat and raise the pressure further.

Now with higher pressure and more heat, the gas enters the condenser. This heat is given off by the condenser to the atmosphere. But since you have an open system from the solar panels to the condenser, the pressure doesn't decrease, only the temperature. In other words the condenser cools the gas, no matter the temperature, back down to ambient. However with the solar panels, this condensed liquid is at a higher pressure. What this means is that the subcooling increases.

A couple problems with your logic. First you say in the solar panel "more heat and raise the pressure" and then in the condenser "since you have an open system from the solar panels to the condenser, the pressure doesn't decrease". You can't have it both ways if its "open" between the solar panel and the condenser how can the heat from solar raise the pressure but the cooling from the condenser not lower the pressure?

You also say "no matter the temperature, back down to ambient" but this is not true because no heat exchanger is 100% efficient. Higher efficiency units help but the refrigerant coming out of the condenser will always be above ambient. If it gains 20 deg in the solar panel it may only be 5 degrees hotter coming out of the condenser but it will always be hotter than if it was never heated by solar.
iknow_t
join:2012-05-03

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said by Corehhi:

I need to find a real world install of this "solar assisted" system.

Doesn't look like much can be agreed on.

there is only 1 I can find, and it's posted in the professional HVAC forum. »hvac-talk.com/vbb/showth ··· sted-A-C the OP DID have 1 installed, and was a disaster, there was a lot of discussion, but the end result was on the last page, it was debunked.