OT Room Air Conditioning Problem III: Control of the Temperature & RH
Further to my post Operation Theater Room (OT) air conditioning system problem part II, today I going to talk about the control of the OT room temperature and relative humidity (RH).
Problem
As you know that the air flow (CFM or CMM), temperature and RH parameter for an air conditioned space is interconnected, or any changes of the parameters will affect the other parameters. The OT room air conditioning system is 100% fresh system make the parameter more sensitive to any changes of the other parameter. This will cause problem to the air conditioning system if the control system for the above parameters is not properly design or set. Precise control of the above parameters is essential in order to achieve the OT room air conditioning specification.
The air conditioning system for my hospital project basically has achieved the design specification (Temperature vary from 20°C~23°C and RH at 60%~56%) after few round of trial and error fine tune setting. However, the hospital operator suggested to reduce the RH further below 55% RH by adding additional heater to the system.
Theory
In my opinion, it is not recommended to do so as it only wasting money. The RH won’t reduce without increasing the OT room temperature higher because heater did not remove the water vapor or moisture content of the air, is the fan coil unit which remove the moisture not the heater. Which mean, if want to reduce the RH the OT room temperature has to be higher, by doing so the my OT room Temperature parameter will not able to meet the designed specification which is not allowed (it depend on the designed air conditioning system capacity, the higher capacity of the air conditioning the more space to let you play around with the control, however for my case it is like this).
Based on my experience, the OT room temperature and RH is not able to maintain fix at one figure example 20°C@55% RH all the time as it 100% fresh air system. It will oscillate within a range. The time for one cycle of oscillation shall depend on the cooling capacity of the FCU and heating capacity of the FCU. Adding additional heater (as suggested by the operator) will only reduce the oscillation cycle time if increase of the temperature parameter is not allowed as per my case.
Conclusion
If increase of the temperature parameter is allowed in order to achieve the desired RH level, why need to waste additional cost? as it simply can be done by set the OT room air conditioning system temperature higher. Please do correct me if any of my view or explanation is incorrect.
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