DeSuperheater flooding condenser?

Hello,


I have a question about desuperheaters. I am doing a remodel and had to move my condenser to a new location. While I was moving it, I decided to install a desuperheater. The DSH is actual the water coil from a previous 5ton geothermal unit, so it is fairly large and should give good thermal transfer. The original plan was just to use it to heat domestic hot water. However, I do have another source of fresh cold water (well and spring both), and thought that once the hot water needs are met, I could switch over to open loop well water and basically have a groundsource ac running. The only caveat is that I would have an extra condenser (the outside air coil) in series after it. I will kill the outside fan if running in groundsource mode.

Assuming I flow enough water through the coil to condense all the ***** back to liquid inside the water coil, will that cause problems trying to flow through the existing air condenser? The outside coil is a carrier microchannel.

Any comments/suggestions would be greatly appreciated.

System details:
Copeland 5ton Scroll
Packless water coil from 5T geothermal heat pump.
Carrier 5ton outside Microchannel Air condenser
Air handler is a 5T Goodman with variable speed.


Thanks in Advance.

Lenny

A desuperheater is just that, de-superheats the discharge gas from compressor without disturbing condensing pressure and system balance. Restrict water flow through DSH for max water outlet temp, without loosing system balance. In approximate terms you can recover around 15 > 20 % of heat from condenser duty dependant on refrigerant used, add VSD to condenser fan as well. What refrigerant is system operating on?.

Its R-22. I also forgot to mention that its a TXV on the air handler.

In my case I would like to use the water coil not just as a DSH, but also as additional condenser area (just like when it was installed as a ground source, since I have a source of water). In this case I would have a much larger effective condenser than a stock 5ton system. My thoughts were to gain additional subcooling and enjoy the standard benefits of of lower pressure diff/more efficient, etc.

Another way to look at it would be like this.. Consider a typical 5ton ground source water condenser. Then plumb an additional air coil in series following it. If the fan were left running, you would effectively have double the heat rejection (10 ton condenser). I would most likely turn the fan off, but the jist is that you have a greatly oversized condenser. Which I think is good as long as the other system components are sized appropriately. (Note, this is where I have enough knowledge to be dangerous, and readily admit it. <grin> )

Another concern I had was the possibility of having so much subcooling that the TXV would be oversized and possibly flood back to the compressor. I'm assuming that the AH has a txv sized for 5 ton now.

Lenny

Too much subcooling will lower liquid pressure and tx valve will not perform correct. Use hp switch to cycle condenser fan but maintain pressure for solid liquid flow to tx. Lowering condenser pressure too much or too quickly will cause refrigerant to become vapour/ liquid mix and you will loose efficiency.. Mike.

Mike,

I understand that too much subcool will cause the tx valve to be oversized, but I'm a bit unclear about "lowering condenser pressure too much or too quickly will cause refrigerant to become vapour/li.....". I'm assuming the pressure across the two series condenser coils will be the same as they are both on the high side of the compressor and before the tx. Are you saying that extra condenser heat rejection will change the pressure along the path of the two condensers, or are you saying that having that much condenser area will lower the total high side pressure? (the latter is what I think you're saying)

Thanks,

Lenny

If your water is cooler than the air, then you will not sub cool, but cause flashing.
Withour knowing your conditions, it is difficult to give you the correct solution

Yes Len, too much condensing will lower highside pressure, and refrigerant will become lazy, so to speak. You must maintain temperature to keep refrigerant as a liquid to tx valve and to prevent the effects of too much cooling causing refrigerant to change state on route. Pressure changes which are "quick", such as events as Mad F has said above, will disrupt system balance and efficiency.... there are 2 words that many of us will call this condition, however, it is taboo to even think of typing the words. Ask STUFUS what voodoo means:eek:.. mike, ( ducking NNN's stare:p).

Hi Mike ref,
hell yes I got slam dunked for using those two words. No, won't even consider typing them.

Hi Magoo, speaking of slam dunk, i saw what mother nature did to Auckland:eek:. Good to see you haven't been relocated and are still with us.. Mike.

Ok, Let me think about this for a bit. I'm still a bit unclear how pulling more heat from the refrigerant via a large condenser can cause it to flash back to a liquid in route to the evaporator. I'm assuming it's because the high side pressure is dropping faster (trying to flash) than the high side temperature is dropping (trying to condense)???

FYI, Here are more details.

- 3.5ton cooling load ( I just did huge remodel and have massive insulation now so I know my system is currently oversized at 5T)
- AH is about 25 feet from condenser
- 5/8 liquid line
- 7/8 suction
- Water source(s) available to feed DSH coil can be one of the following..(D. hot water via side arm heat exchanger, 2-5gpm open loop well water at 52F, 17000 gal swimming pool, hot tub, & 5 300' loops of 3/4 pex in the ground)
- Any type of sophisticated controls are not a big problem. I'm a Electrical design engineer and own a company that designs/manufactures custom circuit board assys, so if there is a way to combat system instabilities or "anomalies" with some smarts on the controller, I'm for that.

As you can see, I have more options than one really needs. Both a blessing and a curse, perhaps.

The goal is twofold.

1) create as efficient as possible A/C system
2) Learn/play with this technology.

Thanks again for all the assistance and interest. You guys rock! I'll start posting pics too showing the coils and controls as I progress.

Lenny

Hi Mike ref,
yes totally weird weather in Auck., fortunately 50kms away from us on the south side. Now two dead.

3.5 t or 12,000 BTU/hr is system capacity, not alot of heat transferre going on there for starters. Lets rewind, hot water system, swimming pool, hot tub? What is the heat source the evaporator is working on? If it's say a 12 by 12 foot room then everything comes to a stop when thermostat cycles off. I cannot see how your system will provide enough heat for your project. Evaporator has to chew on a constant heat source.. Mike.

Mikeref

For now, I'm just running in Air conditioning mode, so I'm pulling heat out via the condenser. The water coil I have will grab 80k btu/hr at 5gpm of 55 deg entering water temp. (This is via the datasheet on the geothermal heat pump that I was running up until three years ago - ) I swiped the coil out of that unit and plumbed it in series with my outside air condenser to use as a DSH. But I realized that I could go ahead and use it as a DSH until my hot water requirements are satisfied, and then switch over to flowing my well water through it and it would be just like my old geothermal except for the fact that there is an air coil following it in series so i was wondering what the effect of that would be, particularly if instead of just pulling the superheat out when heating my hot water, I instead, flow 5gpm of 52F water through the coil and actually condense the refrigerant to liquid "before" it even enters the outside air condenser. I assume that it will flow through without issues.

As to what water source to actually use on the condenser, that is definitely up for grabs. I still need to understand how the refrigerant gets lazy when you over condense and causes system instability. I can slow the water down and prevent over condensing but I would like to run the system as efficiently as possible.

Lenny



Lenny

The if you cond with your well water (which should be good to keep condensing pressures low), then you you feed the cond liquid into your air cooled condensor and the ambient is say 32C, it will cause the liquid to flash as it absorbs
energy raising the condensing pressure, negating the use of the water cooled heat exchanger, basically it is about choosing the correct refrigerant flow, for the correct conditions (mechanical devices driven by some smarts in control)

Mad Fridgie,

Ahhh... That makes sense, I kept thinking the air coil would just remove more heat, but it makes sense that if the outside air temp is warm, it would add heat back and possibly cause the flash. I will be monitoring all the temps across the coils as well as the outside temp, so i should be able to bypass the outside coil if the there is impending danger of flashing back.

Thanks for that description. I was having a hard time visualizing that situation for some reason.



Lenny

what water source to actually use on the condenser, that is definitely up for grabs. I still need to understand how the refrigerant gets lazy when you over condense and causes system instability. I can slow the water down and prevent over condensing but I would like to run the system as efficiently as possible.

Lenny
I see you need to read the thread (started a few months ago) on excessive cooling of condenser. The term i used, "LAZY" really is a loose term for too low of pressure to expansion valve. Take for example a vehicle a/c on a warm day and cabin temp is high and windows are down. When stationary, the a/c struggles as it pulls temperature and humidity out of vehicle and with refrigerant boiled off and vapour left going back to compressor absorbing heat on the way, the compressor has the job of compressing this warm gas which adds heat of compression to pressurised gas for condenser to remove. High temperature in condenser is proportional to high pressure and if condenser cannot remove enough heat, then refrigerant cannot condense to liquid which causes liquid/ vapour mix + high temperature and pressure to be supplied back to TX valve. ( Can go into events which follow later). Now if you spray water onto this overworked condenser, serious amounts of heat is removed, reducing temperature drastically which causes discharge PRESSURE to fall fast, condensing the gas which reduces overall space volume previously taken up by liquid/vapour mix, leaving room for liquid to boil off to accomodate the lost volume untill pressure is returned. So... a certain amount of pressure is necessary to feed tx valve with liquid and fast changes in condensing temps/ pressures make the feed to TX unstable. Too low pressure to TX and it won't work efficiently. Just as incorrect fuel flow to an engine, such as insufficient fuel flow, will cause it to splutter and stop. Lazy is not a recognised term in refrigeration, just a substitute for the "O.C" words that you obviously know or have heard about... Mike.;)

Hi Magoo, looks like Superlen spilled the beans on condensing :eek:.. Sorry No Nick Name, i did not encourage him in any way or form. Still... New Zealand, America, Australia and Japan have had more than enough natural disasters for one life-time...
Attachment 6637 Mike.

Mike,

Thanks again for the great explanation. I'll go try and find that other discussion too. Going to be out of pocket for a few days on a trip, but I'm sure I'll post back with some more questions. I actually was wondering about better control over a TXV (to combat the higher pressure requirements) via software and found out they make electronic expansion valves. Looked handy, probably expensive though.

BTW, I like the "lazy" term. It made sense to me.

Lenny

Lenny,

This thread seems to have petered out several months ago but if you're getting flags on replies, I'd like to collaborate with you on a similar project. After getting two months of 100+ weather and $500 light bills, I'd like to explore using well water (25' down) to cool the condenser on a 4T, R22 system. As an electron herder with a modicum of recall from physics class on heats of vaporization, it seems that if I can reduce the temperature of the liquid ***** from 110F down to say 80 or even 70F, the compressor wouldn't have to work so hard . . . hence, lower light bills.

This mod would also let me move the condenser/compressor unit inside immediately adjacent to the air handler. It seems that our ends and proposed means are similar. I want to eliminate fan and air cooled condenser entirely. A friend of mine about 40 years ago used to have a well water cooled system in his home that produced better than 36,000 BTU of cooling for about the same light bill as I was paying on my 24,000 BTU window unit! I don't know any of the particulars but do recall being jealous of the efficiency!

I'm retired out of the Wichita aviation community and have some capability in circuit design, micro-controllers, etc. I have another refrigeration project to convert a restaurant ice chip maker into a stand-alone kitchen appliance where the pedestal under the ice maker contains an R/O water system along with a water cooled condenser. City water in, one drain, hook up power and presto, my wife has all of her favorite ice she can use.

So the goal is to see if I can get these two systems to work 'all wet'. How's your project coming along?

Bob . . .