Indoor temp 67F, indoor humidity 85%

darrylg

I have AC with Forced hot air (hydronic coil) in the same air handler.
Right now I've been running my gas fireplace and AC at the same time, or changing the thermostat to heat mode to 75 degrees, then cool back down to 67 in efforts to get the humidity below 55%.

Is a whole home dehumidifier the best solution for my issue? Or should I modify the control board to call for heat and AC simultaneously. I realize running the boiler will not be as efficient a dehumidifier, but the natural gas cost may be cheaper than the cost to run the dehumidifier (not to mention the cost of the unit). I also have 2 zones (separate air handlers), so I may need to purchase 2 dehumidifiers.

pecmsg

Any Details????????????

Size of the building?
Location?
Size of the equipment?

darrylg

Living area = 4000 sq ft, single story
Zone 1 covers 2500 sq ft - 4 ton AC 16 seer
Zone 2 (bedrooms) covers 1500 sqft - 3 ton AC 16 seer

Air handlers are American Standard Gold
Boiler is Burnham ESC 6 150,000 BTU

Location is Long Island NY

Most of the humidity issues are on the bedroom side of the house, since there's not much incoming solar heating.

Jamie Hall

Below 55% or below 85%? Makes a difference. Either way the only way to drop humidity is to cool the air to the dewpoint, then reheat it -- either with reheat coils or by mixing with return air -- to come back to the desired target temperature and humidity.

The reason I say it would make a difference is that 55% RH s well within a normal comfort range... so if that's what you're achieving...

darrylg

Jamie Hall said:

Below 55% or below 85%? Makes a difference. Either way the only way to drop humidity is to cool the air to the dewpoint, then reheat it -- either with reheat coils or by mixing with return air -- to come back to the desired target temperature and humidity.

The reason I say it would make a difference is that 55% RH s well within a normal comfort range... so if that's what you're achieving...

Sorry if that was misleading. If I don't supplement with external heat source (either gas fireplace or forced hot air), it will be as high as 85% humidity. I've been able to manage it down to 55% using the aforementioned techniques. Ideally, I think I'd like it below 50%.
The issue is that the techniques I'm currently using are not permanent solutions, I need to actively manage it. I would prefer an automatic solution because I'm not always home.

I guess my questions boil down to, is it stupid to run the heat and AC at the same time (assuming I can get the controller to run them simultaneously)? If so, I'll just go with the whole house dehumidifier.

EBEBRATT-Ed

Something else is going on with you system and you need to get it evaluated by someone that know what he is doing.

#1 is check both AC units and make sure they are up to snuff...air flow, clean coils, correct charge, compressors pumping and pulling full load amps (or nearly so)

#2It's possible you cooling is oversized and shutting down on temp before it dehumidifies the space

#3 check all the ductwork. Every cfm you loose through a leaking or disconnected supply duct you pull unconditioned air=humidity into the space from the outside

Could be other thing too but this is a good start.

And don't run the fireplace whatever you do.

Your sending conditioned air up the chimney...its the same as a leaking supply duct whatever goes up the chimney is unconditioned air leaking in around windows and doors..... it has to to make up for what is lost.To control humidity you need a tight house and any air coming in needs to be conditioned somehow

Jamie Hall

not stupid, but possibly not the most efficient or cheapest approach. If you want the RH to be below 55%, with a room air temperature of 67 F, at some point the air has to be cooled below about 50. Then reheated to 67. Some more advanced air conditioning systems can do this in a self contained way. So do whole house dehumidifiers. So does running the heat, although your AC may not be able to get the air cool enough.

JUGHNE

What is the outside RH% and temp?
How did it work previously....was it always this way?

darrylg

EBEBRATT-Ed said:

Something else is going on with you system and you need to get it evaluated by someone that know what he is doing.

#1 is check both AC units and make sure they are up to snuff...air flow, clean coils, correct charge, compressors pumping and pulling full load amps (or nearly so)

#2It's possible you cooling is oversized and shutting down on temp before it dehumidifies the space

#3 check all the ductwork. Every cfm you loose through a leaking or disconnected supply duct you pull unconditioned air=humidity into the space from the outside

Could be other thing too but this is a good start.

And don't run the fireplace whatever you do.

Your sending conditioned air up the chimney...its the same as a leaking supply duct whatever goes up the chimney is unconditioned air leaking in around windows and doors..... it has to to make up for what is lost.To control humidity you need a tight house and any air coming in needs to be conditioned somehow

Excellent points!

#1 The system was installed in the fall of 2012. How often should I get them checked out?

#2 I'm afraid this is the exact issue, since I don't have much heat load on zone 2, the unit rarely runs. How is this fixed? Right now, I'm just adding a heat load artificially.

#3 This was my initial thought, so I inspected the return ductwork in the attic space this last Spring, and couldn't find any leaks. However I didn't do a proper smoke test.
I do have outside air coming in thru my cellar bilco door, and I will have that sealed up shortly.

Good point about the fireplace, but I have a sealed unit, so it's not an issue. I should have mentioned that earlier.

Thanks for the advice

darrylg

Jamie Hall said:

not stupid, but possibly not the most efficient or cheapest approach. If you want the RH to be below 55%, with a room air temperature of 67 F, at some point the air has to be cooled below about 50. Then reheated to 67. Some more advanced air conditioning systems can do this in a self contained way. So do whole house dehumidifiers. So does running the heat, although your AC may not be able to get the air cool enough.

Correct me if I'm wrong, but I don't understand why the air needs to be below 50? Isn't the evaporator coil the only thing that needs to be below dew point to trap the condensation?
If I run the air temp too cold, then I get condensation on the windows and tile floors.
I believe the dehumidifer works by condensing moisture in the evaporator, then reheats it using heat from the condenser coil.

So instead of using the condenser coil to reheat, I'm essentially using my hydronic coil to reheat.

ChrisJ

Out of curiosity, what kind of temperature drop are you seeing across your evaporator?

Just comparing the air entering the returns to the supply air is good enough.

darrylg

JUGHNE said:

What is the outside RH% and temp?
How did it work previously....was it always this way?

I don't recall the outside numbers when this occurred. Next time it gets that bad, I'll record the numbers. I don't believe it was overly disgusting outside, or it would have been justified.

Yes, it's always been this way since 2012 when it was installed. Over the years I've been changing windows, and I finally have them all changed and still have problems. (sans the fresh air entering the basement door)

darrylg

ChrisJ said:

Out of curiosity, what kind of temperature drop are you seeing across your evaporator?

Just comparing the air entering the returns to the supply air is good enough.

Good point, I'll measure when I get home. I also have a flir thermal camera, so I can measure the temp of the evaporator. What temp should it be around?

ChrisJ

darrylg said:

ChrisJ said:

Out of curiosity, what kind of temperature drop are you seeing across your evaporator?

Just comparing the air entering the returns to the supply air is good enough.

Good point, I'll measure when I get home. I also have a flir thermal camera, so I can measure the temp of the evaporator. What temp should it be around?

I wouldn't trust a FLIR unless you can shoot the return and supply grills with it, and even then it can be iffy.

What the drop *should* be depends on a lot of things. I'm just curious.

Lance

Typical service call. Tools needed. knowledge, and a way to measure the diagnostic indicators. First, is condensate dripping from drain? Look, if not, coil is to warm. Is outdoor unit air flow seem hot on the fan, if not, not doing any work. Two things affect dew point on the coil, air passing thought the coil fins and refrigerant vaporizing correctly in the copper tubes. Whatever affects these two things determines if the humidity in the air passing through the coil will condense on the fins and drain out or not. As for the room air, the source of humidity can be a factor if it is too much for the equipment size installed. If the a/c is working and dumping a lot of condensate then I would suspect a lot of moisture coming from a water source other than outdoor air. I establish air flow first, because if it taint right nothing will balance. Next check the pressures and pumping of the refrigerant and the controls. Air temp into indoor coil can be 15-20F more than air leaving coil. One more thing. If you turn on a properly sized system in a house with indoor temp at 100F and high humidity, with outdoor temp 100f and high humidity it may take three days running before it will cool down enough to reach a dew point to start removing bathtubs full of humidity. Usually the first clue is the folks just got home from vacation.

Leonard

I have a 20k window AC that just about cools the house if I close off the large kitchen, ( it's a bit under sized) . When indoor temp is about ok but humidity is high I run the AC on LOW speed fan.

That way air spends more time in evaporator cooling and condensing out humidity..... but regardless of why ..... it seems to do a good job de-humidfying house without cooling the air too much.

When house is hot and humid I run AC fan on high, it cools the house better but doesn't take humid out as much.


Sometimes ONCE in spring inside it's ~ 70 degs and 95% humidity, so I run AC on LOW fan and fire up the oil furnace to keep house warm. Only happens once every few years, so not worth cost of a dehumidifier for my case.

If your running a fireplace your likely dragging a LOT of outside humid air into house, unless it's one of those super tight insert type ones. The old brick fireplaces were only ~ 10 % efficient at best, sometimes negative 10%

ratio

7 tons of cooling sure sounds like a lot for even 4k ft² of living space. Without actually being able to look at things, my guess is oversized.

You may be able to slow the cooling airflow down a little & get more latent cooling, but that's not really a zero-experience diy project.

Jamie Hall

Thing about evaporator temperature is... so long as it's below dew point, it will condense... some. How much depends entirely on how fast the air is going through it. If the air is zipping through, it won't get cooled and won't condense. And if the unit is running, it's not doing anything at all. As several folks have said, whatever else you do trying to get humidity down, get the system running at a setting which will allow it to run 24/7. If you can -- you may not be able to, but run it as long as possible.

ChrisJ

Jamie Hall said:

Thing about evaporator temperature is... so long as it's below dew point, it will condense... some. How much depends entirely on how fast the air is going through it. If the air is zipping through, it won't get cooled and won't condense. And if the unit is running, it's not doing anything at all. As several folks have said, whatever else you do trying to get humidity down, get the system running at a setting which will allow it to run 24/7. If you can -- you may not be able to, but run it as long as possible.

That's the issue, it's going to be below some dewpoint, but what?

Mine will get near 40 degrees sometimes. My indoor humidity is often in the high 40s, sometimes the mid 40s even with an indoor temp of 68F.

If the system is low on charge, or if the evaporator just isn't pulling down low enough the dehumidification will suffer no matter how long it runs. For example, if he tells us his supply air is 65 degrees, that's not very hopeful.

darrylg

Zone 1 - Supply Temp 55.2F, Return temp = 72F
Zone 2 - Supply Temp = 55.5F, Return Temp = 70.2F
(I may have the nomenclature backwards)

I measured zone 2 right at the air handler, so those numbers should be pretty accurate.
There is condensate in the pan. I could always pump the condensate into a bucket, if that's a valuable measurement?

Outdoor Temp = 71F, 91% RH. It's a rainy day, so I expect the humidity to be high.

Using the dewpoint calculator, with a 55 degree evap temp, the best I can do is 65% humidity? Does that sound right?

Jamie Hall

darrylg said:

...

Using the dewpoint calculator, with a 55 degree evap temp, the best I can do is 65% humidity? Does that sound right?

The physics doesn't lie...

darrylg

I also just noticed that the condenser unit outside is cycling, even though I have a constant call for heat. Is this something I should be concerned about, or is this normal for a low outdoor temp?

ratio

How long are the on & off cycles? How do you know (I'm assuming you meant) the cooling call has been constant?

Is the compressor/whole unit cycling, or just the outdoor fan?

Also, the evaporator will be somewhat colder than the discharge air temp, although a 55° temp doesn't set off any alarm bells.

ChrisJ

That's only a 15 degree drop, which could be normal if the latent load is high. Aka high humidity.

I would expect the actual evap to be a few degrees colder than the air leaving it.

Do you have any idea how many CFM your blower is moving? And how many CFM /ton it comes to?

You can slow the blower down which will make the evap run colder. Anything from 350-400 per ton is acceptable in residential I believe. 400 is considered "normal".

I recently dropped mine from 400 to 380+- and it actually made a difference.

Assuming everything else is working properly, slowing the blower down changes the systems latent / sensible ratio. It will have less sensible capacity so it'll run longer but it'll remove more water. Also, efficiency drops.

EBEBRATT-Ed

@darrylg

If your equipment is oversized you will have difficulty controlling the humidity

darrylg

ratio said:

How long are the on & off cycles? How do you know (I'm assuming you meant) the cooling call has been constant?

Is the compressor/whole unit cycling, or just the outdoor fan?

Also, the evaporator will be somewhat colder than the discharge air temp, although a 55° temp doesn't set off any alarm bells.

Yes, sorry for the confusion. I meant the thermostat was still calling for AC.
While I was taking supply temp numbers, I noticed the temp was increasing.. all the way to 65F. I looked outside and the outdoor fan was no longer spinning. I only noticed this once on each zone, over a 2 hour period. I can monitor it closer, if necessary.
I assumed the fan/compressor go together, since I typically notice a slight power dip when the fan/compressor come back on. The blower was on full, during this time.

darrylg

ChrisJ said:

That's only a 15 degree drop, which could be normal if the latent load is high. Aka high humidity.



I would expect the actual evap to be a few degrees colder than the air leaving it.



Do you have any idea how many CFM your blower is moving? And how many CFM /ton it comes to?



You can slow the blower down which will make the evap run colder. Anything from 350-400 per ton is acceptable in residential I believe. 400 is considered "normal".



I recently dropped mine from 400 to 380+- and it actually made a difference.



Assuming everything else is working properly, slowing the blower down changes the systems latent / sensible ratio. It will have less sensible capacity so it'll run longer but it'll remove more water. Also, efficiency drops.

I'll try to measure the air velocity, then calculate the CFM based on that. I'll get back to you.

darrylg

EBEBRATT-Ed said:

@darrylg

If your equipment is oversized you will have difficulty controlling the humidity

That may be the case. I know zone 1 is not oversized, since it can not keep up in the heat of summer, but zone 2 may be too large. I've tried using fans to get it to share the heat load better, but my house is shaped like a horseshoe, so it's not easy.

ChrisJ

darrylg said:

EBEBRATT-Ed said:

@darrylg

If your equipment is oversized you will have difficulty controlling the humidity

That may be the case. I know zone 1 is not oversized, since it can not keep up in the heat of summer, but zone 2 may be too large. I've tried using fans to get it to share the heat load better, but my house is shaped like a horseshoe, so it's not easy.

Are these two different systems, or one system with a damper setup?

ratio

There are certain applications where the outdoor fan is allowed to stop with the compressor still running, so we can't strictly go with whether the outdoor fan is on or not, but an increasing DAT sure does point to no compressage outside. (It has to do with cold weather cooling operation in case you're wondering.)

There are a number of safeties that could be stopping the outdoor unit, we need to find out if it's that, or the thermostat stops calling for some reason. Next time it happens, go check & see if there's 24 VAC on the control wires in the outdoor unit.

Without running the numbers, you can't really tell if the unit is mis-sized or there's other issues. In particular, distribution issues (i.e. duct sizing &| placement) will cause a correctly-sized unit to misperform. With the average unit being oversized by an often ridiculous amount, I'd take a hard look at the ductwork before I condemned the sizing of the unit regardless of the performance.

JUGHNE

Another possibility for stopping the outside unit could be an electric utility control system that gives them the ability to cycle your outside unit only.
Sometimes these go haywire and have a mind of their own.
Just an idea.

EBEBRATT-Ed

@darrylg

If your supply temps are 55 deg as you stated that's pretty good. Don't confuse supply temp with coil temperature, that's two different things. With 55 deg supply your coil temp is probably 40-42 deg.

I don't have a pych chart in front of me but if your average coil temp is 52 or lower that should get you around 50%rh.

If your not getting that
1. the equipment could be oversized cycling so it doesn't run enough to get the humidity out. A house with oversized equipment is cold and clammy
2. you have a hole in your house that's leaking in too much humidity

3.you have a supply or return duct disconnected or badly leaking

Humidity transfer is not the same as temperature transfer.

Temperature transfer through an open window or door takes some time.
Humidity transfers through vapor pressure and is almost instantanious