Fresh air inlet systems

[kweiss]

Does anyone know the specifics about these systems? I am seeing many of these in new construction and almost all the time they are turned off.

Sometimes the homeowner has turned them off because they were causing the system to run more than they liked. Other times the builders left them off.

I am interested in opinions on the purpose of these systems, the usefulness, the proper settings, etc.

Thanks

[David C. Macy]

I have a question about a fresh air intake that is installed on a 2004 build.

My question is I just need an explanation as why outside air is brought into the cold air return?

Is this what KW is inquiring about? Hope you dont mind me using your thread.

[Bruce M. Graham]

I think this http://www.americanaldes.com/HRVRes.html is what Kevin had in mind. The perception is it cost money to operate and they get turned off. Most homes operate under a negative pressure, bringing in air from every where, doors, windows, fireplace, etc... these units allow you to bring in fresh air in a controlled fashion to maintain a neutral or slightly positive pressure on the home.

[kweiss]

That is a very fancy version. The ones I see most often are integrated into the HVAC system. Generally there is a fresh air vent that is run to the return side of the system and either filtered itself or attached before the system filter. Then there is a control that operates a damper and in some cases the HVAC blower to meet the timer requirements. One name I have seen is Aprilaire.

[Michael R. Boyett]

Kevin, these are sometimes called 'make-up air' devices and are quite common in commercial applications, especially packaged systems. They are designed to intake maybe up to 20% fresh outside air and are adjustable. Like mentioned earlier in this thread, this is beneficial in certain residential and commercial applications where other exhaust sources may result in a negative pressurization of the building sucking in various amounts and kinds of crud. Also, when homes began being built tighter and tighter a few years ago it became advantageous to intake some level of fresh air to replenish the stale, recycled air in the home. I see them from time to time in newer residential applications but simply note their presence and disclaim any ability to judge their operation or performance. I'm surprised one of the HVAC guru's hasn't weighed in, maybe they will soon and give a better description of these systems.

[Greg Veal]

I've seen only one system in a residential setting over the years, and it was installed in the home of a mechanical engineer friend of mine. His system was elaborate and expensive, as it was designed on a commercial scale. A real overkill, which I kidded him and still do today.
Keep in mind, were not talking F/A or C/A into the system here.
That being said, there are residential systems out there that are certainly capable of giving the same basic effect as the commercially designed systems. I think the major consideration in installing any type of make-up air/ economizer/ fresh-air system is in the design, location, application and control of the operation. There are various design criteria, that should to be evaluated on a case by case basis (ie: structure design/methods of construction, insulation, vapor barrier, infiltration, usage, etc.) as well as the local environment. You don't want to be intaking outside environmental conditions, that can't be filtered adequately. Controlling the operation is critical, either by timers, thermostat, enthalpy, etc.
Any design or installation flaw, lack of proper maintenance, etc. can/will be more problematic to the owner/occupants, the structure, and the contents, than a more typical designed HVAC system.
Sorry if I seemed to ramble, but I hate to see design, installation mistakes and/or misapplications, just for the sake of dollars or wanting to be the latest/greatest on the block.