Im commissioing a new installation on a project in wherby the
repository / bookstores have to be kept at 16 DegC and 55% RH.
Now then, the rooms are sealed and have a door mounted pressure relief.
We are supplying the rooms with 95% recirculatedair 5% is conditiond
fresh air makeup. We are allowing for 5% losses through the relief duct
in an effort to keep the space positvley pressurised.
The fresh air make up runs through an ahu with the following (essential
only) components, Frost battery, Cooling Battery, Heater battery, steam
External air comes in at this time of the year at around 22 DegC 78 %
This fresh air (5%) is supplied onto the recirc air handling units
serving the repository.
The repository units contain 4 coils and a humdifiers.
cooling, heating, for sensible load and then cooling / heating for
The units have been running for a month but i cant get the %RH level in
the spaces below 60% it should be 55%.
The return air coming back is at 16 DegC (therfore is at setpoint) and
the humidity is at say 67%.
We are controlling the coils on return air and therfore as you can see
there is a demand for dehumidification.
The secoond cooling coil actuator (latent load) has wound fully open in
an effort to do this, this drops the temperature off the coil to 7
DegC. Therfore the reheat coil comes into heat it back up to the
required calculated setpoint this fluctuates depending on the extract
air deviation from the room SP setpoint which has settled out at 15.7
Anyway the % RH off coil is around 95% and following the reheat it only
drops to 70% it appers as though the air isnt any dryer.
Ive worked it out pyschrometricaly and although the RH hasn't change
the moisture conent has. But the consulatnt isnt intrested in moisture
content only RH I have no idea where to go from here. it should be
noted that the sensors we are using are specialist and have been pre
calibrated. I have checked there positions and redings whilst point to
point commissioning. Also the coils in the ahu have correct pipework
portings and the coils are positioned in the correct way. Finally the
steam humdifier remains isolated.
Any suggestions will be appreciated.