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StuartF84
19-11-2013, 08:27 PM
I'm planning on expanding a phase change system to have a second and eventually third evap. I need a way to direct refrigerant (r404) to the various thermal heads on a duty cycle depending on each head's heat load and set temp. I'm thinking that the best way to do this is with solenoids and a cap tube manifold. A three-way solenoid would work for a dual head system. I'd like to keep it quiet if possible as the solenoids would be on a 10 second or less duty cycle. Would a servo be better? Can anyone recommend a solenoid, i've seen that LEDEX has some that are supposed to be quiet but I don't know if they would work with 404.

Any help is appreciated.

frank
19-11-2013, 08:39 PM
Assuming that you have a fixed speed compressor?

If you split your 'Evaporator' load into 3 and then control the amount of flow into each circuit by solenoid valves, how are you going to control the compressor and condenser duty when, say, 2 of your evaporators are not requiring any cooling (sol valves closed) ?

StuartF84
19-11-2013, 08:52 PM
I should have mentioned that the the heads have heater cartridges in them controlled by a independent PID loops. I'm using the solenoids to minimize the work required by the heaters. When two heads are not needed all of the refrigerant will go to the one that is active. The compressor is a fixed speed 1/4 hp.

frank
19-11-2013, 09:04 PM
Any chance of a sketch or drawing?

install monkey
19-11-2013, 10:01 PM
if your reducing the capacity of the evaps the you need to derate the outdoor unit- by means of an inverter drive or unloaders on the heads on bigger stuff

StuartF84
20-11-2013, 12:04 AM
10940
high side = 1/4" pipe
suction line (purple) is 3/8"
accumulator to compressor (blue) is 5/16"

Using r404a we need to get down to -55C and would like to go as high as 200C being able to handle at least 300W at 0C. We've gotten down to -57C, i haven't run it up past 150C yet as our prototype evap was soldered not brazed.

High side pressure is roughly 150psi and suction is around 15" Hg Vac.

install monkey
20-11-2013, 10:44 AM
I recommend a solonoid on the liq line before the evap to pump it down if your goin to 200 deg

StuartF84
20-11-2013, 07:53 PM
You don't think leaving the hot gas valve wide open will be enough?

install monkey
20-11-2013, 08:40 PM
not if your taking your coil upto 200deg
in low load conditions youll be operating on 1 coil and your compressor is suddenly well oversized- your tev will be sized to 33% of the outdoor capacity
also you dont want any refrigerant in the evap if your heating your evap/conditioned space to +200deg
check your pressures:rolleyes:

mbc
24-03-2014, 05:27 AM
solenoid valve on the liquid line before the evaporator to pump down it and also you can use (CPR) crankcase pressure control in suction line near compressor to protect you compressor from over load in starting time.
I am sure you can use in 15 Hg vac. might you have to change spring inside CPR.