Not Cold Enough in Tuberculosis Lab 2

[Kinemenematics]

Hi, I work at a hospital with a simple 4hp, Ceiling Concealed Fan Coil unit serving a small 50 sqft room, oversized of course.
And yet, it's too warm inside (27'C) for staff comfort...(21'C - 24'C is desirable).

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AIR PATH:

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FRESH AIR IN -> EVAPORATOR -> HEPA FILTER -> BOOSTER FANS -> 10ft DUCTING -> DIFFUSER -> EXHAUST OUT


QUESTION:
Can someone tell me why it's warm inside? The AC is already oversized for this room and yet the air isn't cold. My bet is the HEPA FILTER at the air intake being clogged up, but I've been told by the maintenance crew that they've recently changed the filter. Compressor has been changed with a new one and serviced too, The only other thing I can think of is the thermostat which is old but it's set at 16'C and hasn't been swapped. Whole system is around 9 years old.

 

[LittleInch]

If the booster fans are your only means of air flow then it is likely they are in the wrong order and should be first in line. Fans find it very difficult to lower pressure to induce flow, but are much better at providing increased pressure to blow air through things. Either move the fan or instal a second one upstream the evaporator.

Where is the condensor on all of this? Or are you taking a cold water supply?

What is fresh air temperature?

Have you temperature readings downstream the evaporator?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Drazen]

what are the proofs that ac unit is oversized?

 

[marcoh]

First check you airflow to make sure you are getting the airflow you required and at the same time measure your supply air temperature.

I would suggest the AC is grossly oversized and is limited to the number of starts/hour.

 

[EnergyProfessional]

Why is the filter downstream of the evaporator?
If the air going to cooling coil is unfiltered, all the particles in the air will settle on the wet coil and grow funny things - not ideal in a hospital or anywhere else.

you should measure airflow and DAT to see if the unit operates as designed. As for oversizing, how do you know? Did you perform a load calc?

 

[willard3]

There isn't enough data to answer the OP's questions.

To start, get a velometer and measure airflow.

 

[chicopee]

In addition to the above responses, is it possible that the 10' long duct is in a warm surrounding?

 

[dbill74]

Can someone tell me why it's warm inside?

The simple answer is more heat is entering the space than leaving.

Adding to the things to look for that have already been mentioned.
Maintenance personnel lie and exaggerate, "recently" could be 4-12 months, time to change again.
The compressor was changed out; check your refrigerant levels.
-Could be refrigerant was fully replenished, different refrigerant, or there is a leak.
What assurance do you have the new compressor is same capacity as old? If it is of sufficiently different size, the coil could be freezing.
Did hospital staff add or change any equipment in the room? Have they changed what they do in said room?
How many people are in the space when it's warm? Does this match sizing calcs for the FCU?
Take temperature and flow measurements around the FCU to verify it is actually cooling.
Might not be one thing, could be a combination of things.
How long has this been an issue? Start looking at things that changed when the temperature started being a problem.

Hope this will give ideas of things to look for.
Good luck, let us know how it turns out.

 

[ChasBean1]

For the compressor to work, there can be an airflow proving switch. Try reversing the tubes on the airflow proving switch.

 

[Kinemenematics]

Thanks for the input, this is all really helpful.

The Fan and primary air filter should be upstream of the Evaporator coils.. And it makes sense that the primary air filters may have not been cleaned

One thing for sure, is that the problem was not always there. It surfaced only recently, so I'm gonna poke a little bit more to find out. At least now I know where to look.

As for data, I'll go take the measurements.

Will be back!

 

[Kinemenematics]

I have an airflow meter and a wind meter (see below). Without access to the ducts, it's impossible for me to slot the airflow meter's tube into the straight sections for a more precise flow volume & velocity reading. Is there some kind of employable correction factor to adjust for this if I were to take the readings at the diffuser? Would a windmeter be better?

Also, wouldn't parameters like Compressor running Amps and Supply air temp be more relevant here?

Fluke 922

http://www.fluke.com/fluke/uken/hvac/iaq-tools/air-testers/fluke-922.htm?pid=56154

Wind Meter

http://kestrelmeters.com/products/kestrel-1000-wind-meter

A colleague of mine took infrared readings of the diffuser with a Fluke 62 Max IR Digital Thermometer, and it read 30'2 C. It didn't feel 24'C when I last stood in that space, but 30.2'C sounds almost ludicrous.

Any ideas?

 

[berkshire]

Kinemenematics
To take an accurate reading at the diffuser you really need an airflow hood, those things are not cheap Starting at $1500 for a low end unit, rapidly going up to above $4000. You may be better off getting a test and balance company to come in and measure your register outputs for you, or if you know how to use an air-hood , seeing if you can rent one somewhere.
B.E.

You are judged not by what you know, but by what you can do.

 

[LittleInch]

This might sound stupid, but did this problem only surface when they changed the compressor recently?. Are you sure it's going the right way around? 3 phase motors can easily be mis wired or mis connected, turning your cooling system into a poor heating system?

I would start with the cooling system first and make sure it's connected properly, filled with the right refrigerant and actually doing something. Temperature of the air coming out of the condenser would be a start point. something like a faulty pressure sensor on the cooling circuit could be causing the compressor to cycle on and off more than it should.

Work out if you have cold liquid first before you start looking at the air system, but a blocked evaporator might also be indicated. Plenty to check...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.