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Old 01-18-2010, 08:17 AM   #31
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humidity question


Your area doesn't have a constant 90%outdoor RH.

DFW area has as much humidity as your area. They can get the humidity to 50%.

Always possible you just haven't seen a mold problem yet. but its there.
Few mold problems, are actually heath problems. But you can't tell the difference just by looking at them all the time.

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Old 01-20-2010, 12:35 PM   #32
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humidity question


It's kind of funny that on the one hand you diagnose my "problem" as having a leaky house, but then you turn around and tell me that more "fresh air" is the solution...

Yesterday the average humidity was 90%, and my wife had the windows open... Day before it was 76%, then 78%, 95%, and 82%. Those are daily averages, not highs.

I've never lived in the DFW area, so I really can't comment on what it might be like to do so.

According to this website:
http://www.sercc.com/climateinfo/historical/avgrh.html

Our average annual morning RH is 86%. If you have the windows open overnight in the more pleasant months and the average annual morning RH is 86%, how much do you figure that helps to lower the indoor RH?

There is no mold problem in my house. Sure, there are mold spores. There are mold spores in every person's house.
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Old 01-20-2010, 05:19 PM   #33
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humidity question


Outside fresh air is for when the heat is on.

Opening the windows to let fresh air in when the humidity is high. Is why your house is never at or below 50%.

A home can have 50% or less RH in YOUR area if that is what the home owner wants.
You may not offer that to your customers. Or want it for yourself.

But, it is possible. And not that hard.


PS: Your average afternoon humidity isn't that high. We have as much here.
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Old 01-21-2010, 09:08 AM   #34
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humidity question


I used to live and work at Myrtle Beach AFB as an HVAC engineer. One of my projects was to modify the control system for the bowling center to keep humidity below a certain leve, I think we started out with a throttleing range of 50 to 50%. The design of bowling centers is such that there is a large percentage of outside air, it then travels down the lanes and exhausted out the back. This center had no conditioning of the lanes other than this flow of outside air. We added a humidistat that would turn on the AC , up to all four stages running, but at least one more stage than the thermostat called for. Reheat would prevent the temperature from dropping. Well during the summer that sucker ran the AC full bore most of the day, with the boiler humming along pretty often as well. Only on the hottest days when near peak design did it run on thermostat alone. We changed the setpoint to 55 and 60% but it still ran most of the time. Especially during league bowling with lots of people perspiring. And if you think this is bad, it would not maintain setpoint when the sea fog would roll in. This was all done becuse the bowing center management complained about high humidity levels.

At that time the base was paying for the utilities, then regulations forced them to pay for utilities out of the lane rental, and snack bar proceeds. After their first bill they asked why their bill was so high. We told them their AC was running almost constantly to control humidity. So they requested that we remove the humidistat. Their summer bill was almost half after that.

So it maybe realistic to be able to control humidity, but the cost may not be realistic. At least not in very hot and humid climates.
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Old 01-21-2010, 02:24 PM   #35
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humidity question


Using a bowling alley with a 100% outdoor air unit as an example when we have been talking about residential homes. Is comparing apples to watermelons.

Now. How much did it cost them to repair the lanes. After they left the humidity get out of control.

Around here. Bowling alley's control humidity to protect the lanes. Not to make the people more comfortable.

Why didn't you just use reheat pipes on that system. It would have been a very economical way to dehumidify the fresh air.

Practicality is dependent on the method used. You obviously weren't using the right method.
Take a look at how grocery stores in your area control their indoor humidity. If they don't they can loose not only product. But compressors.
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Old 01-22-2010, 09:55 AM   #36
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humidity question


Using a bowling alley with a 100% outdoor air unit as an example when we have been talking about residential homes. Is comparing apples to watermelons.

It wasn't 100% outside air, more like 20 to 25%. The outdoor air is high because of a large number of people doing moderate excercise. But that doesn't really matter because the AC was designed to condition that extra outdoor air at peak design. But there is a lot of humid air when off peak.

Now. How much did it cost them to repair the lanes. After they left the humidity get out of control.

Nothing. Keeping the humidity down helps improve play, especially on the approach lanes. As well for comfort. Never was high enough to cause excessive swelling of the wood. And I believe the next time the lanes were to be resurfaced they planed to replace with synthetic.

Why didn't you just use reheat pipes on that system. It would have been a very economical way to dehumidify the fresh air.

Not sure what you mean by reheat pipes. We did use reheat. Heat pipes would have recoverd some (not all) of the heat but could not use them because the air was exhausted on the other side of the building.
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Old 01-22-2010, 02:57 PM   #37
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humidity question


I did work in some bowling alleys.
They had problems with the alleys if they were above 55% too often.
If they reached 60% or . We had too slowly bring the humidity back down


Reheat pipes have nothing to do with how the buildings air is exhausted.
And would have eliminated the need of heating the air with another source.

Desiccant wheels would also have been far less expensive to use.

So basically. It was an incorrectly designed/engineered system, for its purpose/job.

Sorry. But it seems your spending so much energy on justifying not controlling humidity. That you overlook how it can be done. And just say good enough. Too much work to do it right.
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Old 01-22-2010, 04:44 PM   #38
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They had problems with the alleys if they were above 55% too often.
If they reached 60% or . We had too slowly bring the humidity back down.

The manufacture required that we condition the space to those requirements. This would have required conditioning of the ally and with about 3 times the area would have been 3 times additional energy instead of dehumidification of the regular space with less that one times the additional energy. ASHRAE said it was unneccessary, that exhausting the outside air down the ally was enough. Although their requirement was 55% at what ever temp it was wood doesn't react with relitive humidity but absoulte, The constant airflow should have keept the absoulte humidity well below the level that corrosponded to their reqirement. The lanes were not under a warranty so we ignored that requirement. They never had a problem with the lanes other than a sticky approach on humid days, and no problems when we were using the humidity control.


Reheat pipes have nothing to do with how the buildings air is exhausted.
And would have eliminated the need of heating the air with another source.

Desiccant wheels would also have been far less expensive to use.


Please explain what a reheat pipe is. Heat pipes need an exhaust stream right next to the intake. Dissicant wheels were new at the time (late 1980's) as I recall you had to use two or three in a row in such a humid area and only saved a small amount of energy, you still had to use natural gas to dry them out. I doubt we had the space. We typically had to use 8 row coils and 250 Cfm per ton to get humidity down.

So basically. It was an incorrectly designed/engineered system, for its purpose/job.

Other than the contractor using a poor coil, and the unit not wringing out as much moisture than we wanted, it worked beautifully and did exactly as we wanted. It was designed to ASHRAE standards. I have noticed that most bowling alleys also do not bother with such excessive requirements. Perhaps we could have used some energy saving devices but I doubt they would have payed back their cost in less than ten years, they may be much cheaper and energy more expensive.

The base closed about 6 years after we did this and the building is now abandoned. So those energy devices and the expense to condition the lanes would have been a waste of money.
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Old 01-22-2010, 05:00 PM   #39
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humidity question


Heat pipes.
Are basically. Pipes(loose finned coils) connected to each other. And are positioned on both sides of the evap coil. They contain refrigerant. The warm incoming air is cooled by that refrigerant absorbing some of the heat. The refrigerant vapor them is forced/drawn to the colder coil on the discharge side of the evap coil. Where it is re-cooled. And then as more liquid in the inlet side pipe vaporizes. The newly cooled liquid then moves to the inlet side.

The reheat pipes precool the air coming into the evap coil. Allowing the evap coil to remove more moisture then if the air came in the higher temp.

There is at least one company making their air handlers with this as a factory installed device. And many grocery stores, are now using it also. And using other configurations of it.
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Old 01-22-2010, 05:05 PM   #40
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humidity question


How long were you still at that base after you disconnected the humidistat.

Since you said next time they were going to resurface with synthetic. It doesn't sound like you were there too long after you disabled the humidity control.


PS: We run as low as 100CFM on 100% fresh air units at times.
Some other systems with humidity concerns and only 30% or less are ran as low as 200 off of VFDs. And then increase CFM as the humidity drops.
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Old 01-22-2010, 05:31 PM   #41
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humidity question


How long were you still at that base after you disconnected the humidistat.

It was put in about 87 or 88, I left in 91 and I believe the base close 93 or 94. The humidistat was disconnected about a year maybe two years after it was installed. None of the bowling alleys in the area was conditioning the alley per manufactures requirement, I toured them before we did this. They used about the same method but some used many unitary units instead of one commercial unit. I think one was doing some conditioning but it was not enough to meet the manufactures requirement. I think we were using 40 tons and about 10,000 to 12,000 CFM total air.

They were planning to resurface with synthetic, but that was before anyone announced the base was closing. I doubt they ever did.

PS: We run as low as 100CFM on 100% fresh air units at times.
Some other systems with humidity concerns and only 30% or less are ran as low as 200 off of VFDs. And then increase CFM as the humidity drops.

Yes you can run down to no air with chilled water, this was a large DX system, not sure what the lower limit is for DX. I not working HVAC now, more of a project manager these days. But with 100% outside air it would be a lot lower. But now I am in Atlanta units for normal recycled conditioned space are running closer to 400 CFM per ton.


Last edited by H. Phillips; 01-22-2010 at 05:34 PM.
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Old 01-22-2010, 05:46 PM   #42
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I was talking about DX(direct expansion) systems at 100CFM per ton. We have to at some places to keep the humidity controlled. But use VFD's to increase CFM during low humidity times.

Some malls are now switching their stores over to no min fresh air. And controlling air quality by CO2 sensors. CO2 reaches X PPM the fresh air damper opens 100% until CO2 is back down to X PPM.

They find it that their mall fresh air system is enough for the stores. Until the stores get full. Then the stores CO2 sensor takes care of any problems by controlling the stores fresh air system.
This greatly reduces the humidity in the stores. And the amount of energy the store uses to cool their areas.
This is in malls that have a central system. And the stores by their heating and cooling from the mall, or both the mall and stores by from a third party.

One mall has reduced their cooling load by 1300 tons on average with this method. They seldom need to use all their chillers anymore.

50% of the time, a single 1150 ton chiller can handle the entire mall. And they keep their humidity under control. No 60% RH in the place.
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Old 01-29-2010, 09:29 PM   #43
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humidity question


House was at 55% with painting, mudding the closets
In 3 days it dropped to under 30 % again
Another 6-7 days of cold dry air has moved in
Both humidifiers running again

And the heats been going pretty steady today
Single digits the next 2 nites, not warmer until Monday
Man I love New England............not

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