Adding hot gas to txv, increase capacity of system

[acsupertek]

I've heard you can add hot gas to the txv to increase load and system run time.
Can any one tell me how this is done?, and how do you regulate the hot gas to the TXV valve?

[service guy]

Yes you can use hot gas bypass, but my first question is what is the application and what kind of equipment do you want to install it on. sometimes hot gas is not the best option as were unloaders are a better fit. let us know!

[acsupertek]

This is a 38AQS016 carrier split heat pump, 06D compressor electronically unloaded. The problem is the system is oversized for the space it serves and the humidity is high. Replacing this system with the proper size is out of the question. I am trying to find a way to increase run time without cooling the space below 74-75 degrees. Re-heat is also not an option.Any help or suggestions would be greatly appreciated.

[bku46]

Yes, you can install hot gas bypass, After your compressor unloads and the load is at min, hot gas should energize as your last stage of cooling before unit shuts down. You may have to contact the manufacture as for size of hot gas setup.

[agrv8d]

Gotta love it. I'm not going to give you any options but it better work.

[seaboard]

Adding hot gas bypass won't be cheap and may not solve your problem. You'll have to tee into the discharge line. Add a solenoid, bypass regulator valve and replace the TXV distributor assembly to accomodate the bypass. Your evaporator coil will run at a higher temperature and may not be cold enough to remove the humidity anyway. Have you slowed the fan speed to the lowest you can get away with? This is a much cheaper solution to your problem.

What is the new heat load versus what this unit is rated at? Can some cooling be dumped elsewhere?

[service guy]

It's difficult to dehumidifiy a space properly without a reheat I think in this case hot gas bypass would not be the best option, I think the customer would be putting alot of cash into something that he/she probably will still not be satisfied with JMO.

[cynic]

Dunno if hot gas would be a good idea on a heat pump. does the unloader actually work ? I have seen more than one carrier that had something stuck under the unloader solonoid right from day one keeping it fully loaded. if it has 6 cylinders would the piping allow another stage of unloading ?

[airworx]

you tee in just past the txv with a mixing tee, remove and change orfice, install a check valve. hot gas would be set to feed at around 56 lbs unloader set at 58 lbs. but i think your better off talking to carrier tech support and see if theres anything that can be done. adding another unloader to this machine is not an option if im correct theres only 2 cylinders. i would make sure unloader is set properly and set the differential a little higher.

[sonc]

You don't have to go through your ******* to brush your teeth.

Electric reheat with scr probably your best bet here.

[acjourneyman]

You add an EPR valve and a solenoid valve which is teed off of the discharge line, pipe it over to the evaporator after the expansion valve and you are done.Set EPR valve to 58# and parallel the solenoid valve to the liquid line solenoid valve, assuming there is one.If there isn't omit the solenoid valve,should work fine for your operation but is an energy hog.Oops, didn't realize it was a heat pump, I have never seen HGBP on a heat pump and don't have a clue if it would even work.

[Edited by acjourneyman on 09-24-2004 at 10:53 AM]

[cxagent]

In theory, HGBP should work on a heat pump. In cooling mode the evaporator pressure is low and the HGBP opens to prevent the pressure / temperature from getting too low. In heating mode, the evaporator pressure is high and the HGBP should never open. That's my theory anyway.

I suspect there may be some issues with oil return, overpressuring the HGBP valve, etc. that would create major problems. I wouldn't want to be the one to test for problems in a customer's facility.

Why is reheat not an option? You said this is a heat pump, any chance you could bring the heat strips on for dehumidification reheat? This might be as simple as wiring a humidistat to the strip heat contactor. That is assuming this unit has strip heat installed or you can get electric power to them. This might be cheaper and easier thanthe HGBP. Just a thought.

[quin]

acsupertek,
recommend Trane reciprocating refrigeration manual
excellent book, my bible,
installed properly with hot gas you will never bust another compressor from liquid slugging.
hot gas only increases capacity of condensor not evap.
hot gas is misunderstood by many & used by fewer.
accumulators& EPR's are band aids
Hot gas will increase refrig. velocity when load is less than capacity of compressor.
loaders & unloaders are good but compressor unloaded at a saturated evap coil refrigerant velocity too low for oil return. Get the book I'll check back later for any questions. ask about sporland aux. side connectors
every cap tube will mesure exact same temp.
good luck !
remember the kiss rule
Quin the eskimo

[airworx]

one thing i forget to add is you do not gain efficiency you lose it.