Blower on delay for better humidity control?

[54regcab]

What are your thoughts about delaying the blower turn on for about 30 seconds so the A-coil has a chance to get cold? Would this result in significantly lower humidity during part load conditions?

[iszell]

If the CFM is set correctly for the appropriate btu and the chagre is set according to proper conditions, would it make a difference in humidty contol if the blower has a 30 sec delay seeing that the system has been commisioned for optimal effeciency? I belive that a properly commissioned A/C system will remove humidty and perform much better under any load condition.

[BaldLoonie]

Seems to me ICP used to do it that way. Or some variable speed systems offer slow start as one of their dehum profiles.

[teddy bear]

A 30 sec delay makes a very minor differecnce in the amount of mositure the ac removes. It's more important to have a very cold coil to remove moisture from the air. The length of cooling cycle is also very important. The cooling cycle must be long enough to saturate the cooling coil and pan and allow a significant amount of moisture to go down the drain. It takes 20-40 mins for moisture to start to drip to the drain. Coils hold +1lb. of moistue per ton before they start dripping to the drain. At the end of cycle, all the moisture on the coil evaporates back into the home. So time delays are a few drops. When the outdoor dew points are +55^F without significant cooling loads, a good dehumidifier is important for good humidifier is important.
Regards TB

[BaldLoonie]

I have a chart somewhere based on data given to me by the product manager of a major brand as high SEER (12-13 back then) came out. While an oldie might have said evap very cold after 5 minutes, a newer unit with big coil and higher suction may take 10 minutes. So more critical than ever not to oversize. We often suggest downsizing based on our calcs, our nearest competitor tends to want to go bigger.

[Mr Bill]

It takes 20-40 mins for moisture to start to drip to the drain..

Were in Arizona? We installed a Ruud system with a N-coil on Monday, system had been down for 2 days, 10 minutes of start up was producing a lot of water running through the T, you could look down into the T with your flashlight and the T was half full it was moving so much water.

[zarathos]

From what I've learned on time delays on cooling, they are on to remove moisture off of the coil, to help reduce the possibility of mold. That is what I was told from Carrier when I asked about their 5 ton RTU fan delay.

[teddy bear]

We installed a Ruud system with a N-coil on Monday, system had been down for 2 days, 10 minutes of start up was producing a lot of water running through the T, you could look down into the T with your flashlight and the T was half full it was moving so much water.

I tested several dry coils with 75^F, 50%RH with similar results. A/c down for two days in Huston is probably very high indoor %RH with result in much more moisture in the air removed than <50%RH where a controlled space is.
Try a dry coil and the space 50%RH, report the time. I did a VS a/c on low speed last week, took 45 mins, to start dripping. The unit removed <3 lbs. per hour on low speed. At the end of the cooling cycle, the moisture evaporated back into the space. If the cooling cycle is <45min.,after re-evaporation back into the home, no net moisture will be removed from the home.
Regards TB

[Mr Bill]

Try a dry coil and the space 50%RH, report the time..

Yes I have to admit, it was 100° outside with probably a 80% RH.

[LKJoel]

I have a chart somewhere based on data given to me by the product manager of a major brand as high SEER (12-13 back then) came out. While an oldie might have said evap very cold after 5 minutes, a newer unit with big coil and higher suction may take 10 minutes. So more critical than ever not to oversize. We often suggest downsizing based on our calcs, our nearest competitor tends to want to go bigger.

I agree, I'm a big fan of under sizing, on the right job

[Danae12]

wow all this high tech formula talk.. Make sure it has a txv, before even dreaming about a delay...



I have seen some very retarded stuff the past year and a half...

[ironpit]

Under sizing or over sizing based on your load calcs?

Aren't load calcs supposed to be accurate? Is there a calc for under sizing and one for over sizing?

If so, why have one for correct sizing , if correct sizing is wrong, which would then be understood that the over and under size calcs are correct, even though they are wrong?

Or do we just put in a system that is wrong according to the correct load calc?

Is that right?

[ironpit]

Where's bunny? She would love this!

[billygoat22]

some of the variable speed units have a dehumidify mode to drop the blower speed the entire run cycle- activated by a dehumidistat.

my mom's house has a little control from Lennox- you set it for dryer and it kicks over a relay to drop to a lower blower speed- but you could use a regular dehumidistat and relay to get the same effect. drops a psc motor to the next lower speed.

both of these increase dehum, but only when the unit is running. and a txv would be a better setup if the airflow is cut well back.

won't work on a cool day when the a/c only runs 5 min/hr at a time. That's where a whole house dehum would come in.

[billygoat22]

Didn't central city hvac do a custom setup yrs ago?