ReplyI would just check for condensation at the coil, if it's pulling out condensation, that's where you'll see it.
Measure RH, see if it changes.
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I am going on a call monday that space is 60%. And floors even become wet. I will check charge airflow thermostat location run time etc. Is there a way to determine that unit is pulling out proper amount of moisture. I guess psychometric chart. This unit has been there for quite a few years. It does a MRI room.
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I would just check for condensation at the coil, if it's pulling out condensation, that's where you'll see it.
Measure RH, see if it changes.
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Collect the condensate water and weigh it. I think you want to have about 3 lbs. of condensate output per hour per ton of capacity.
Measure the return air temperature and compare it to the suction pressure converted to temperature. The suction temperature needs to be 30+ degrees below the return air temperature in order to dehumidify.
If all the refrigeration numbers are correct - you will have to reduce air flow to get it.
PHM
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Originally Posted by hvac17011
PHM
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When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
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When humidity is an issue, there are three main factors.
One of them is not to accept that this has been fine for years. Local flooding, excessive rainfall, and moist air masses can bring the humidity load to a point where the unit cannot keep up.
Something has changed.
The other points are:
Overcapacity, where the setpoint is reached too quickly. Was the equipment changed?
Fan speed too high. Was a blower motor changed?
Along with PHM's ideas, this should get you thinking "big picture."
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We do pms there. Another tech said unit was working ok I am going to go to dig a little deeper.
I work on alot of large desiccant dehumidifiers. They are designed to remove a certain amount of grains. I know exactly what I am looking for. Unit i looked at today was designed for 2grains/pound. Is there any way to know something like that on a regular rooftop or split system
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Remember the moisture removal is a by product of Air Conditioning. There not designed as dehumidifiers.
Check the water output as PHM said.
Check the air flow
Check static pressure
Charge
Get the design specs and compare them.
Are all make up and exhaust fans operating according to specs?
You could spend several days troubleshooting this!
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It being an mri room it could have a reheat coil or something.
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A lot of the MRI rooms I take care of have separate humidifiers feeding the area. Check that one of them is not out of control range.
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I second the reheat idea.....it should have one.
also, if you work with dehumidifiers, it's the same principal....just mechanical instead of desiccant.
use your psychrometer to get your process points and plot it on the chart.....sometimes it's hard to get to the duct for the measurements on RTU's, so do your best to get accurate supply and return numbers. this is where an in duct psychrometer comes in handy, you can just drill holes in the duct as close as possible to the unit.
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Aside from checking the unit for normal operations, I'd be looking at the outside air intake, like maybe an adjustment on the economizer for the fresh air.
Maybe a balance issue was changed, could have been intentional or not. Someone may have decided to bring in more fresh air, on a system that was not designed for that load.
I do a triple evac with nitro to remove non condensables.
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Has the heat load changed from the original design?
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Yes. Yes it has.
I do a triple evac with nitro to remove non condensables.
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The manufacturer should be able to tell you how much water by design it should pull out of the air under normal conditions. The room likely has a humidifier check and make sure it is working correctly
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The discharge temperature verses the room temperature will tell the story. If you look at the psyc chart you can easily see that for example if you have 55F discharge temperature and 72F room temperature your RH is around 50%. If the room temperature is 65F your RH is around 60%. The water content is the same. Those measurements tell you where to look if the water content is per design. If the supply and room temperatures are within design and the RH is high you are getting water from another source.
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Wayne is on the right track. Lets say the room temp is 75^F, 60%RH, a 60^F dew point. The cooling coil must supply air that is 5-10^F lower dew point to reduce the moisture in the space. So check the dew point in the space and the dew point of the supply air. 75^F, 60%RH, a 60^F dew point, the a/c supply needs to be 50-55^T dew point. To lower the dew point of the supply, slow the air flow of the air going through the cooling coil. This works good with an a/c cooling coil. If you have a chiller, you must lower the chill water temperature to increase amount of moisture removed from the space. Also measure temperature of the floor condensing moisture. Floors must colder than the dew point of the air above the flow. IF there is a cold space below the floor, insulation or warming space below the room may be necessary.
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A proper installation and evacuation of and air conditioning system begins. A vacuum gauge is used to determine the level of atmosphere (degassing If the atmosphere that you are removing from the refrigeration system is moisture laden, as that Leak rate is simply derived from a drop in vacuum over a unit of time,
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OP is referring to moisture removal from the air side (dehumidification), not evacuating a system for refrigerant charging.
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https://m.youtube.com/watch?v=OjYoNL4g5Vg
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I think I would get supply and return WB & DB temps along with CFM. Do the math for both total heat and sensible heat, subtract the 2 and you get your latent removal. I believe it should generally be about 30% if it is less you need to start looking at what would affect that.
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I know this stuff but have to look up the particulars. The bear not only knows this stuff but has it all committed to memory so when he talks listen.
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