Added continous ventilation, now I have drafts

[BenjaminM]

I used ASHRAE 62.2 to guide me in adding continous supply ventilation to my house. I'm using a Panasonic inline fan to blow 90CFM of air from a good outside source into the duct system just upstream from the main blower in the return plenum. I can damp the inlet to control the flow from 120 CFM down to whatever I need. According to 62.2, with a stack-effect credit I need 90CFM from a fan.

After I did a lot of work to seal duct leaks in the vented crawlspace, the system is working exactly as designed. The house is slightly over-pressure, which I intended because we're in Radon Zone 1 (3.9 pC/L on 90 day test), and we have a mild climate and low humidity year round (Nevada) so I'm not concerned about excessive condensation.

Since the system began to work, there has been complaints of cool drafts. The house is heated to 70-72 F 24 hours a day (we have babies), but the cool flow from the supply registers is noticeable. When the cool air comes in from the vent duct, it drops the return air plenum temperature down to around 50 F (without the main blower mixing house air). By the time the vent air reaches a supply register, it has warmed some. Air temperature near the supply registers is around 68 (4 degrees cooler than the room).

Assuming the flow from the 11 registers is roughly equal, that's about 8 CFM from each register minus whatever is coming through the return grill when the main blower is not running.

The supply registers are located on the floor around the perimeter of the floor plan. They have metal diffusers.

How can I reduce the feeling of drafts? If I replace the Panasonic fan with a HRV, it will warm the incoming air a little bit, but it would still be perceptibly cooler than heated room air.

Ventilation, in my mind, necessarily requires the movement of air. Is it possible to move the air in and out without creating the sensation of a draft?

What would be better to reduce the feeling of a draft? An HRV to warm the incoming air, or working on better diffusion?

An HRV is expensive and the temperature differential here is not enough to recover the cost for 15 years or more (twice as long as we expect to own the house). Nevertheless, the cost is "doable" for comfort reasons if in fact it will stop the drafty feeling.

Any other suggestions to make ventilation work without drafts?

[pmeunier]

This may be what you're looking for:

Temperature Sensing Duct Heaters

* Completely programmable duct sensing electric duct heater.
* Automatically senses air temperature within ductwork
* Regulates electric heat output based on predetermined desired temperature.
* Flexible temperature ranges from 40 – 100 degrees

EM-WX0111R 1 kW/3414 Btu/h 120V plug 6” Round Element
150 cfm

http://www.electromn.com/res/html/duct.htm

see pictures and assembly:
http://documents.northwrite.com/Shelter/ductheaters.pdf

disclaimer: I haven't tried those and don't know anyone who did...

[BenjaminM]

Thank you. That is an excellent suggestion. Although I'm concerned about burning up to an extra kilowatt during the winter, I estimate such a heater would cost me about $100 a year. That's competitive with HRV costs for 6 years or more (I plan to own the house for 7 years), and an HRV doesn't guarantee incoming air will be warm enough without additional heating.

I like the concept, but it's not very clear how to buy one or what the sale price is. Searching the Internet for duct heaters, I found only high-powered ones for sale.

I already have a Honeywell TrueSteam humidifier on order. I won't be sure how well it will warm ventilation air when the main blower is idle until the installation details are worked out, but I'm going to get that in before I decide anything else. Presently, we're running three 4-gallon room steam humidifiers with the humidistats at 35% RH. I'm hoping the 9 gallon/day TrueSteam will take the load off them.

Following popular guidelines for ASHRAE 62.2 standard ventilation using a continuous ventilation fan and integrating the system with the main ducts has proven less than ideal. If I wasn't determined to maintain a little pressurization, I think it would work better to only cycle the main blower to avoid building up a volume of unmixed ventilation air in the ducts. I can see that continuous ventilation really calls for an independent system of lower volume ducts in the conditioned space that might also recirculate some air to aid in mixing without having to run the main blower.