Have you looked into putting in a Rawal Valve?
I have a customer that has a 10 ton trane controlling air temp coming off a dessicent wheel. This is maintaining temp/humidity in a vault. They run the dehumidifier all year. There is a bas system controlling outdoor unit. The unit is maintaing 55 degree supply air into space. The problem is during the winter months when the dehumidification load isnt alot the outdoor unit will not run well.Th unit will run for 1 minute shut off for 20 sec come back on. There isnt a very big deadband or time delays which could be improved. The unit is a standard 10 ton trane with ranco head pressure control. The unit has hot gas bypass running to evaporator. They have a standard txv installed. The unit has run 4-5 years like this probably wont last forever. My thoughts are to run compressor all the time and bypass to maintain supply air temp. I was thinking of changing to exv. My question is what would be the best way to control this. Can you use standard hot gas bypass or do you need liquid injection. If you use standard bypass valve how do you control superheat at compressor.
Have you looked into putting in a Rawal Valve?
I wasnt sure if that would reduce the capacity enough. We do install them.
If the proper valve size is selected it should work. But, you can't reduce the capacity any lower than 50% or oil not getting back to the compressor could cause bigger probelms
Is there any way to add an economiser and set it up that during cold temperatures you get free cooling? This would bypass the mechanical system and the need to modify it during low ambient conditions.
It kinda sounds like your cycling off of low pressure switch.You got a wheel in unit I'm guessing 100% out side air.
work to live not live to work.
Oops. "standard" Trane, it probably is cycling on low pressure. If its just doing it on start then a low pressure bypass timer would help the situation. Bypass it and let the suction pressure settle in.
its shutting off because control system removes call. supply air setpoint has been reached. its running 60# suction not going off on lp.
Whats a exv? Electronic expansion valve?
aNtHoNyNoZ,
I have attached an artilce on the EXV.
I was thinking that when I was typing but did not add it.After two or three times it locks out.I was also wondering why it has a fan cycler when there hot gas.How far can you set dead band?Either way on a minute and off twenty sec and back on better check bas or senser.
work to live not live to work.
Hot gas has many uses, capacity control, humdity control, controls compressor short cycling, etc. Fan cycling is used to maintain discharge pressure. So the 2 are used for 2 seperate purposes. Hot gas bypass is generally set to maintain 55-60#s of suction pressure. It will inject hot gas straight to the evaporator to maintain suction pressure. Generally they inject hot gas after the expansion valve and before or at the distributor. This allows the TXV to feed and the superheat will still be maintained by the TXV even though you are sending more gas to the evaporator. This eliminates compressor short cycling on low suction conditions.
Since the system is cycling on space temp, the best bet is going to be a Rawal device to reduce the capacity. We have used this in many instances and if sized correctly will help control.
To address the post above about adding an economizer, the unit already is bringing in fresh air with an energy wheel and this will in no way help with Humidity control in cold weather.
To the OP, keep us posted on what you do decide to do and how it turns out.
Stay safe.
Jim, that is why there is hot gas to falsify load, to keep head up,just wondering why fan cycler and yes I understand there is a heat wheel. I have worked on many with heat wheels and the units never had econimizers on them,they were 100% fresh air intake.
work to live not live to work.
check with Trane to see if they have a "low ambient option" you can retrofit. They stop the condenser fans.
Elsewhere on this site a person named "Lambo" wrote:
01-07-2011, 05:09 PM
Below are excerpts from the attached Trane RAUC manual. Based on the original low ambient options intended for this unit, I would contact Trane for advice regarding the use of over-the-counter head pressure controls.
Low Ambient Dampers
Low Ambient Dampers are available as a factory installed
option or can be field-installed. Dampers are used to extend
the operation of these units from the standard operational
temperatures to a minimum of 0oF without hot gas bypass
or 10oF with hot gas bypass. (These values apply when
wind speed across the condenser coil is less than 5 m.p.h.).
If typical wind speeds are higher than 5 m.p.h., a wind
screen around the unit may be required. By restricting the
airflow across the condenser coils, saturated condensing
temperatures can be maintained as the ambient temperatures
change.
The low ambient damper actuator controls damper modulation
for each refrigerant circuit in response to saturated condensing
temperature.