RHOSS EXP TXAEY intermittent hp fault

[AndyHX]

Hi guys , this is busting my balls!
does any one have any experience on these units??
if you dont know, this is a heat pump that can work in 3 modes , water to water (taking heat from chilled water system and adding to heating system ), water to air (chilling water ) or air to water (heating water) so all good , great for saving energy and redistributing heat where it is needed in building.
The building began operation on a partial load and we started to have problems , at first we thought because of light loads mostly heating and small cooling for computer room.
System has been tripping manual hp switch about once a month.
After resetting hp we monitor system for a couple of hours , we notice it will at the moment have priority to heat water (coming out of winter here ) and will take heat from chilled water system first, then when chilled water to temp it will switch to air to water to heat hot side then when chilled comes back up it switches back to getting heat from chilled system so it is doing alot of chopping and changing between modes.
There is also a totally seperate chiller on the chilled system that i have only seen work when the heat pump trips out .
I have checked all water flows through system and they are all up to spec and we have tried shutting the water flow down and this does trip the flow switch so i do not think it is water flow related .
The system has 2 reversing valves in series and a number of solenoid valves on liquid lines , bit of a headache to look at and try to fiqure out..


http://www.rhoss.com/index.cfm?metho...d=51&classe=23



Any help or advice would be appreciated. im going out tommorrow as it has tripped again. its been about 3 weeks, so ive never seen it trip , had my guages on it , never gone over 400psi , its a r410a system.
who knows??

[Mick13]

if u say its not caused by lack of water flow as it would cut out via the flow switch first, perhaps its tripping on the water to air cycle (when acting as a chilller) when the fans are removing the heat, maybe one of the fans is tripping on an internal overload or something similar after a while running and driving the head pressure up.... check if any of the fans seem to be getting hotter than they should?

also are the fans more than one speed? maybe theres a problem with one of the speed relays....

just a thought.... iv had a similar problem

[AndyHX]

Thanks Mick ,
im going to put a second hp switch on the system to check whether it is actually tripping out at 42 bar. The 2 fans all seem to be drawing recommended amps etc.

[Mick13]

good idea....

i had a problem a while ago with a unit tripping head pressure occasionally, similar to what your experiencing, however it was just an APAC split ducted system, i would attend site and reset it, and it would run perfectly.... anyway after being called back a few times and seeing it work perfectly every time, i went right through it and checked everything....

they use a solenoid to send hot gas to the metering device end of the outdoor coil to de-ice the coil, rather than the reversing valve.... this system was set up with electric heaters for heating and didnt even have the rv wired up so it has no need to ever go on defrost, anyway i disconnected these solenoids and never got called back again....

So im assuming there was either a sensor or PCB playing up and energizing those solenoids when running on cooling mode, hence sending discharge gas into both ends of the condenser coil, with nowhere to go it would trip the hp switch in about 5-10 seconds.

Perhaps u have a solenoid that is not opening when it should and causing some sort of similar problem? u mentioned the pipework is quite complicated (as i imagine it might be).

my scenario might have absolutely nothing to do with your situation, but if its anything like i imagine, there would be solenoids or something similar to route discharge gas to the air cooled condenser or water cooled one, so perhaps one is sticking shut and the gas has no where to go?

let me know how you get on

good luck!!

[AndyHX]

Just added a schematic of refrigeration . Went to site today and unit had tripped mcb .
rhoss.12.gif

[AndyHX]

Situation resolved . It was a bms issue switching off a pump but flow switch not tripping.