cheap window reverse cycle ac build

[AC_Hacker]

Originally Posted by jeff5may

...The only thing I really have left to do with this unit is to figure out whether it puts out enough heat below 40 degrees to justify running it. I do know that it annihilates my gas heating bill down to around 30-35 degrees, depending on humidity...

Sounds like a hybrid system would work well in this situation, with a modest ground loop being used when the air temperature gets cold enough that the COP drops. Then, you could switch into GSHP mode until the too-cold air period has passed, and back to ASHP.

Using this kind of setup, your loop field could be much smaller than if GSHP was used exclusively. And, since the thermal hit on the ground loop will be intermittent, with substantial resting periods in between, the loop temperature would have time to recover.

You could build an integrated unit with solonoid valves being automatically switched, and all. But the easiest would be to get another air conditioner and dedicate it to GSHP. Then select the appropriate system based on the air temperature.

This is not my idea, but it seems to be finding acceptance in situations where funding is limited, and efficiency is desired.

Don't know about you, but I fit that criteria.

Best,

-AC

[jeff5may]

I already have plans for another unit. It will have a massively oversized outdoor heat exchanger in it. By the way the new, "super-efficient" heat pumps look, that's the route the OEM's have gone.

The only problem with this approach is balancing the flow of the multiple paths of refrigerant. With a super-sized outdoor coil, it doesn't make sense to use only one path for the plumbing: pressure drop and flash gas don't play well together. Once you get enough liquid into the evap inlet, it tends to "burp" its way through the long line, rather than boiling off nice and gently. The coil quickly frosts up where the expansion zone is, insulating the area and making the effect worse. In cold weather, the coil tends to frost up where the heat transfer happens and the rest of the surface is largely inactive.

Having parallel flow paths kills this effect much the same way as the exhaust system of a car. Once the refrigerant splits up, the separate flow paths operate somewhat independently of each other at lower individual flow rates. If one path burps, the overpressure within that path is absorbed by the other paths. The result is more even heat flow over a larger area of the surface. In cold weather, the coil takes longer to frost up. When it does, much more of the surface has to become covered before heat flow suffers.

My next unit will most likely be a split unit. I'm considering using water or vodka as a secondary refrigerant also.

[NiHaoMike]

Originally Posted by jeff5may

Later that evening, my neighbor behind me asked me why I was still running a window a/c in the heating season. He was concerned that i may have killed it last night! How embarrassing.

He has never heard of a heat pump?

[AC_Hacker]

Originally Posted by jeff5may

...My next unit will most likely be a split unit. I'm considering using water or vodka as a secondary refrigerant also.

Please explain...

-AC

[jeff5may]

In ground-source systems, the primary refrigerant is the phase change material and the secondary refrigerant is the ground source liquid. Whether you are running a pump-and-dump system or a recirculating loop, the heat pump transfers its heat by way of the secondary refrigerant. This secondary refrigerant is then either disposed of or recirculated through your massive ground loop.

This is also true of hydronic systems on the indoor side. A refrigerant-to-liquid heat exchanger is employed in the heat pump to transfer heat with the liquid that is then delivered to the area where heat is in demand. In a hydronic heating system, the secondary heat exchanger is actually the floor, slab, radiator, wall or whatever.

Direct-exchange (DX) systems are named as such because there is no secondary refrigerant used in the process. There are more types of DX exchangers than only refrigerant-to-air, but they earned the label since they are so popular for space heating and cooling in forced air systems. The most obvious example is the pump-and-dump system described in the first paragraph. Even though it is technically a direct-exchange system (since there is no secondary heat exchanger), the ground water is still considered a secondary refrigerant.

[jeff5may]

The next unit I put together will probably be a split unit. Since it will most likely be filled with propane or propylene, I want to try to keep all the primary refrigerant outdoors. The unit will be air-source, since I rent and cannot legally drill up my back yard. It will look like a normal split-system outdoor unit, but will not have copper lines running indoors.

The unit will have a "grossly" oversized outdoor heat exchanger. I plan on finding a 3 to 5 ton outdoor unit and running it with around 1-1/2 to 2 tons of compressor. This should give me lots of COP outdoors.

On the indoor side of the circuit, I plan on running a coaxial or plate heat exchanger that will use a water-based secondary refrigerant. For antifreeze in the winter, I plan on using ethanol. The refrigerant lines running into the house will contain this mixture. If I use a tank for this solution, it will have the pump in it, supplying the exchanger with ambient indoor liquid.

[AC_Hacker]

Originally Posted by jeff5may

...This secondary refrigerant is then either disposed of or recirculated through your massive ground loop...

Are you sure that you are using the correct terms?

My understanding is that a refrigerant is exploited for it's phase-change characteristics.

This from Wikipedia:

The simplest refrigerant is water. Non toxic, low cost, and widely available. The simplest cooling systems, known as swamp coolers in the south-west United States, do not even need power for a compressor, merely a blower fan - evaporated water is simply vented to the living space, where it serves to increase humidity also. However, drawbacks are multiple and severe as well. The total cooling power of the unit is limited by the fact that neither coolant nor air is recirculated. A swamp cooled home will have a constant supply of fresh, not too-dry air, but if the air outside is already humid, cooling power is severely limited. This is why such units are not found in areas of frequent and high humidity, such as the south-east United States. Furthermore, if the temperature outside is severely too hot, such as over 110 degrees F or 43 °C, the unit will not cool the air sufficiently for comfort even if the dew point outside is very low.

In your example, you are using water for its heat carrying potential as a liquid, and only as a liquid.

I understand that water can be used as a refrigerant (R-718), but when it is, it used in a phase-change context.

-AC

[jeff5may]

Read this article:

Refrigeration Service Today: Primary v. Secondary Systems | Refrigeration content from Contracting Business

Mine will operate like this one, only instead of a tank containing the primary exchanger, I will use a BPHE or coaxial exchanger with an overflow tank, much like an automobile radiator.


Obviously, it will contain a reversing valve and other control components.

[AC_Hacker]

[QUOTE=jeff5may;33921]Read this article...


OK, I did read your article. In every instance in that article, when they are describing how the system works, they are using the term "refrigerant" when they are describing the primary side, and the word "coolant" when they are describing the secondary (non-change of state) side.

On some of the Extreme phase change hacking sites, there are some uber-hackers who really are successfully building series refrigeration systems that have two separate loops, each with their own different refrigerants, each going through a change of state to accomplish Extreme goals (amazingly cold CPUs).

But I don't think your scheme qualifies as dual refrigerant.

I also noticed that you direct-linked to the diagram, so I was able to see that it came from the UK.

In my opinion, the diagram is either wrong, or UK centric.

I further suspect that if you use the term "refrigerant" when referring to "coolant" in communicating with academics, engineers, or trades people in the USA, you'll experience misunderstandings because you will be using a term in a way that that is not generally agreed on.

Now, I'm not suggesting that you stop using it that way, in fact I write poetry and I put great value in bending and twisting and inventing new linguistic glimpses into this dreary point of view that gets called 'reality'.

So, good luck in this undertaking.

Best,

-AC

P.S.: Subsequent to this post, I called my local refrigeration supply house, where I buy my tools and supplies that I use.

I talked to Tom, the guy who works the counter, and has been ringing up sales to the HVAC techs in town for the last 18 years. I figure that Tom is a better authority than the UK artist that did the diagram...

Tom agreed with me.

[jeff5may]

Ok, here's another:

Mechanical cooling equipment

all you never wanted to know about refrigerants in 1 document:

http://www.ignou.ac.in/upload/Unit%204-32.pdf

You call it a wall, I call it a bulkhead. It's the way they taught me in the Navy. Either way, it's hydronic. I don't mind if you call it coolant. Tom the reefer man can call it whatever he wants to. Engineers probably call it six different things over the course of a week.

Water is used extensively as a primary refrigerant in ammonia absorption (or is it adsorption?) systems, the kind used in RV refrigerators. Guess what? It don't change phase. In lithium bromide absorption systems, the water does change phase. In both systems, water is considered a primary refrigerant not because it changes phase, but because it's inside the primary refrigeration system.