useing frig for ac

[obxdave]

I heard that you could use a frig to chill water to run though a water to air heat exchanger does any one know of this thank you for your help

[Ryland]

Where is the heat from the fridge going? also where is the heat from the pump, the friction of the water flowing in the pipes and all the other losses?
All of the energy that a system like this is going to use is going to be turned in to heat, add to that the fact that a fridge is just a heat pump with half of it inside of an insulated box, you are pulling heat out of that box and that keeps your food fresh and cool, the wast heat and the heat that was pulled out of the fridge escapes in to your kitchen, part of why kitchens are one of the warmest rooms in the house.

[Piwoslaw]

Originally Posted by obxdave

I heard that you could use a frig to chill water to run though a water to air heat exchanger does any one know of this thank you for your help

Yes, you can do that, but it would be more efficient to delete the water part and directly chill the air. Plus, as Ryland mentioned, you'll have some spare heat to deal with (in fact, you get more waste heat than you get chill), so if you divert that to your hot water tank then it'll definately be worth it.

[AC_Hacker]

This is an interesting thread...

Originally Posted by obxdave

I heard that you could use a frig to chill water to run though a water to air heat exchanger does any one know of this thank you for your help

obxdave, I wish you'd included a bit more detail about where you're going with this, but...

Yes, you can use a frig or probably more correctly a vapor compression machine to chill water, and then use the water as your transport fluid to carry the heat (or cold in this case) to the place where you want to use it, as you said through a water to air heat exchanger.

Originally Posted by Piwoslaw

Yes, you can do that, but it would be more efficient to delete the water part and directly chill the air.

Piwoslaw is correct that you might be better to go directly from refrigerant-to -air, as you pay a penalty (somewhere around 10%) every time you go through a heat exchanger. In this case you pay the penalty when you go from refrigerant-to-water (10%) and again when you go from water-to-air (10%).

But there are cases when you can't do that, like if you have a centralized vapor-compression machine and you want the heat (or cool) ofice space twenty stories away.

Originally Posted by Ryland

Where is the heat from the fridge going? also where is the heat from the pump, the friction of the water flowing in the pipes and all the other losses? [NOTE: this usually runs below 5% (-AC)] All of the energy that a system like this is going to use is going to be turned in to heat, add to that the fact that a fridge is just a heat pump with half of it inside of an insulated box, you are pulling heat out of that box and that keeps your food fresh and cool, ...

Ryland has a good point of view here because he is considering not only the cold that is produced, but also the heat produced by the vapor compression process.

...this brings up another point that is worth keeping in mind, which is in a vapor compression process where the heat produced is of primary concern, like a house heating heat pump, the heat from the work of the pump is adding to overall efficiency.

But in a vapor compression process where the cold produced is of primary concern, like a refrigerator or an air conditioner, the heat from the work of the pump is subtracting from the overall efficiency.

Originally Posted by Piwoslaw

Plus, as Ryland mentioned, you'll have some spare heat to deal with (in fact, you get more waste heat than you get chill), so if you divert that to your hot water tank then it'll definately be worth it.

Yes, so long as the heat from the frig condenser coils is at a higher temp than the water tank. If the tank is a pre-heater, the temperature difference would defrinitely be greater, so the heat would flow easily. If the tank is the water heater tank and the temp was set high, like maybe 120 F (49 C) it might lower the efficiency of the frig.

Originally Posted by Ryland

...the wast heat and the heat that was pulled out of the fridge escapes in to your kitchen, part of why kitchens are one of the warmest rooms in the house.

Or at least 200 to 300 watts warmer. The stove is really a BIG heat maker.

But consider this: in the winter, when it is cold outside, we use heating to raise the temperature of the house, then we use a frig inside the house to lower the temperature of the inside of the frig box, and the vapor compression not only has to fight the home heating system, it also has to fight off the stove when we are cooking, and it also has to fight its own compressor which is throwing off heat! There's some serious inefficiency there.

Maybe feeling warm and comfy about how the frig keeps us warm, is misplaced gratitude.

Personally I don't think there's anything sacred about a frig... We need to take a whole new look at how we keep food cool, especially in the winter.

Sure, we need to keep food cool in the winter, but do we actually need to use a vapor compression machine? By most estimates, the refrigerator is the largest energy consuming appliance in the home (this is not counting a furnace or a water heater).

Maybe what we need is to use our local climate in a way that uses outside air to do the cooling, and perhaps a bit of inside air when it gets too close to freezing.

Any thoughts?

-AC_Hacker

[Ryland]

We are getting off topic here, so maybe a new thread should be made?
The idea tho of using outside cool/cold to keep your food cold is not new at all, but how do you do it without a net loss? because it have a net gain you need to start with a fridge that is better insulated then your house and you might say that your fridge has better seals and as much insulation as the walls of your house but if we think about the crude idea of just cutting a hole in the back of your fridge and bringing in cold air, you now have all 6 sides of your fridge that are sucking heat out of the room, in other words you have more surface area, but on the other hand the heat that is given off by the fridge is electric heat and if you have gas heat or wood heat in your house it might be cheaper to make up for the small amount of heat loss with gas heat.
I really like however the idea of using the waste heat to heat water, trouble is thatmy understanding of how fridges like to operate it's at 70F or so, get them to hot or to cold and they don't work as well, that is why the fridge in an unheated garage is going to drive your electric bill way up.

[Patrick]

Originally Posted by AC_Hacker

Maybe what we need is to use our local climate in a way that uses outside air to do the cooling, and perhaps a bit of inside air when it gets too close to freezing.

Any thoughts?

-AC_Hacker

How about diverting outside air through the condenser coil in the winter?

[Piwoslaw]

Originally Posted by Patrick

How about diverting outside air through the condenser coil in the winter?

Why not year round? In the summer you will get slightly worse efficiency since it'll be harder for the coils to lose heat, but you'll gain efficiency from using the A/C less. If the coils could be somehow mounted on the outside wall (north wall would be best), then their size wouldn't be limited by the size of the fridge. Coils 2-3 times larger would be more efficient.

Put those coils in groundwater and then you'd see improvement. Doable with a GSHP.

[AC_Hacker]

Originally Posted by Piwoslaw

Put those coils in groundwater and then you'd see improvement. Doable with a GSHP.

I measured the temp of the condenser coils yesterday and got readings in the 95 to 110 F range. My kitchen temp was about 65 at the time.

So this would suggest to me that using the coil temp to directly heat the water heater tank won't work so well, but if there is a pre-heater tank, with cooler water, it would work.

I know my ground temp is generally 50 to 55 degrees F (with seasonal swings) when you get down a meter or two.

So, it would certainly improve the efficiency of the reefer, and the low-grade heat put into the earth could be re-harvested with a GSHP.

In this case, the ground would be like a giant storage battery.

Sometimes, if there is water migration through the earth, the water carries away the stored heat. The other side of this is that it brings new ground-temp heat...

Regards,

-AC_Hacker

[benpope]

From builditsolar.com:
Cold weather passive assist refrigerator - It uses a heat pipe as a "one way valve" to move heat out of the fridge when the temperature outside is cooler than inside the box.
Hot water cold beer - Uses an AC compressor to move heat from a beer keg to a hot water tank.
Ice box - a new take on the old-school ice box, it has a heat pipe similar to above, but uses the heat draw to freeze 300 gallons of ice. He says it takes 10 days of temperatures below 20 F to freeze the water. Then he shuts off the heat pipe so that all of his food doesn't freeze.
Edit: More on heat pipes

[AC_Hacker]

Good going BenPope,

Here's a link to a DIY Heat Pipe page!

Regards,

-AC_Hacker