[rjordan392]

The thing that comes to mind to most people when they think of air conditioning is just cold air coming from a register. This is not so. All need to be reminded that the term means that the air is filtered and then conditioned. Its the conditioning part that is overlooked by more then just a few. What I am getting at, is that the homeowner or technician should check for a fresh air intake when servicing the system. There should be a fresh supply of air introduced to the system using ductwork directly to intake side of the furnace. If the house is well sealed and no fresh air intake is installed, then all that is happening is circulation of stale air. For years, I complained to the serviceman about the comfort level and it appeared to be humidity related along with the smell of mildew. My homes humidity level was building up faster then the system could remove it. After I installed a fresh air supply using 4 inch duct, it made a big differance in the comfort level. For what its worth.

 

[mdshunk]

It is also quite possible that your system was oversized. Your situation is a common symptom of oversized cooling equipment. The cooling setpoint is satisfied before much humidity is removed. Bringing in fresh air without any control can be big trouble in many climates too. This is what an enthalpy control is for. A blanket recommendation for unmodulated fresh air is not a wise recommendation either. Glad it worked out for you for the time being.

 

[rjordan392]

I"ll check with my HVAC technician if he gets any requests to install an enthalpy device on a residential system. One other point I did not bring up was that the fresh air is needed to dilute indoor air pollution and that a means be provided to exhaust stale air. You are right that controls should be installed. Did you know that in a well sealed residence without any fresh air intakes and no stale air exhaust and about 1600 square foot of living space with about a family of four will have a carbon dioxide concentration of 1000 ppm or above? I live alone and the concentration is 540 ppm indoors when all doors and windows are closed. The outside CO2 concentration is approximately 340 ppm. This also means that all other pollutants are at higher concentration then the outdoor concentration. So there is a lot to air conditioning then what a lot of people realized. Techicians who specialize in industrial and commercial air moving systems are most familiar with air pollution and CO2 and its effects on the working enviroment. So its not just a blanket statement, its just being ignored by homeowners who know about it and by the technicians installing the equipment.

 

[mdshunk]

I"ll check with my HVAC technician if he gets any requests to install an enthalpy device on a residential system. .

I think you already know that he does not. I'll even venture to say that the average residential tech doesn't even know what an enthalpy control is. They are a standard feature on commercial systems.

If the humidity outdoors of your house was so much lower than indoors, where is all your moisture load coming from? You say you live alone, so I don't suspect that showering and cooking play much into your situation. My gut tells me to look for some masonary mass that doesn't have a vapor barrier like a basement wall or floor, or possibly an overly damp crawl space, roof leaking down inside a wall unseen, etc. You said in an earlier thread that your house was 18 or 20 years old. Your house isn't built that tightly if it's that old. The moisture is infiltrating from somewhere, and that is the root cause of the high indoor humidity. Adding outside air is only a stop gap corrective measure.

Plus, indoor air quality is not ignored in the residential market. Air to air heat exchangers/heat recovery ventillators are often pitched by HVAC salesmen. Homeowners often don't bite because of the cost. You didn't just stumble across this fact on your own. It's been discusses and addressed in the marketplace and in the field for decades. People just don't want to pay for it.

 

[HVAC Doc]

People just don't want to pay for it.

MD, you nailed it on the head there. Even in new construction, trying to get the builder or owner of a new home to pony up an extra $500- $1000 to install an HRV or ERV is like trying to get a rooster to lay eggs. Another nice thing about ERV/HRV units is that many have filters to help clean the air before introducing it into you home and also have exchangers to temper the air so you don't pull in 40 deg. air into your toasty 75 deg. house and make your system work harder. many also have dampners that open only during run cycles so that you aren't just venting your conditioned air to the outside adding to system run time as well.

 

[rjordan392]

My residense is 50 years old. My row homes front and back wall are not insulated but while doing some repair work, I did notice a poorly installed vapor barrier placed over the brick. I used to have a 120 gallon fish tank in the basement which did not help matters but my residense always had an uncomfortable feel to the air before I installed the tank. Then soon after, I installed the fresh air intake and the differance was quite noticeable. Fresh air is only suppied when ever the furnace blower runs in addition to any air leaks in the structure. The total interior cubic footage that is air conditioned is about 11,400 cubic feet. I have a 2-1/2 ton system. Right now I believe I got the humidity and/or bad air problem somewhat solved as my relative humidity is 55 to 58 % in hot weather and my residense is much more comfortable then in the past. When the HVAC technician (the owner) was consulting with me, he did check the compressor for its rating and did not mention that it may be too big or too smalll for my residense.

 

[mdshunk]

... he did check the compressor for its rating and did not mention that it may be too big or too smalll for my residense.

Since I obviously can't look at your house and do the Manual J calc, my rules of thumb tell me that your system may be 1/2 ton oversized. It is possible that bringing in outside air does little more than add load to the system to cause it to run longer and remove more humidity.

Don't get me wrong. I'm pleased that this solution of yours seems to have solved your problem in your house. I just want to point out that among the solutions that will solve your problem, this fix of your ranks fairly low on the list.