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Thread: Should I keep my ERV?
10-30-2005, 07:56 PM #1Regular Guest
- Join Date
- Oct 2005
Hi folks, new to the forum. Looking forward to participating.
I was going to ask "what is the best way of wiring/running my ERV", but after searching some previous threads, I wonder if it is worth having at all.
First, some background.
We just built a new house in Central Massachusetts. Two-story, about 3000 square feet, four bedrooms, full basement, spray-foam insulation. Lots of good windows (Anderson 400-series) and 9 skylights. We have two independent HVAC systems (one for each floor) consisting of a propane-fired furnace/air handler/AC. We also have a central vent fan (FanTech) that vents all three bathrooms. The builder was going to put in a couple of fresh-80's to allow fresh air into the house (and relieve low internal pressure from the bathroom fans), but we didn't like the idea of spending so much money on building a tight house just to drill a few big holes in the wall. So instead he installed a FanTech SER1504 ERV. Since it was something of an afterthought, it was ducted into the cold-air return of the upstairs air handler, and wired so that the furnace fan would run whenever the ERV ran. The contol was a FanTech control, but it ran primarily off of humidity, when we wanted it to run for x minutes out of each hour.
Let's just say that I wasn't happy with the system. Because the contol was ineffective, we ended up leaving the ERV on all the time, so the furnace fan ran all the time. I suspect we could have used the fresh-80's and used less net energy.
I thought it would be nice to have the ERV kick on anytime the furnace fan did, since the times of year we are concerned about indoor air quality are the times of year that the windows are shut - the times we are running the AC or the heat. But I haven't figured out how to wire that setup. It isn't covered by the FanTech literature, and my HVAC guy wasn't too helpful.
But now I'm wondering - is this system (from a whole-house perspective) actually what we want? I'd love to hear opinions about how you would have designed the system differently, and what we might do now that we own what we do.
Thanks for taking the time,
10-30-2005, 08:18 PM #2
No reason why the ERV cannot kick on with a rise in humidity in the winter and no reason why it cannot be wired to come on everytime the furnace runs.
If it was ducted to draw air from humid sources then supply fresh air to the return duct work of the furnace it would pressurize the duct work and fresh air would spill out everywhere, in particular out of return vents when the furnace fan was off.
The ERV should give you year round fresh air without overdrying the house.
10-30-2005, 08:28 PM #3Regular Guest
- Join Date
- Oct 2005
Thanks for the quick reply.
1) It was ducted to draw air from the cold-air return to the furnace, and supply fresh air to the same cold-air return, just about 10 feet downstream. That is why the furnace fan needs to run whenever the ERV runs.
2) How would I wire the ERV to kick on with the furnace fan? The ERV requires a pair of terminals to be shorted to run. Would I need a current sensing device around the power lead of the furnace fan? Or a pressure switch in the duct?
10-30-2005, 09:37 PM #4
That kind of ducting is a last resort to fix a winter humidity problem. Something that would get retrofitted to an existing home, usually not used in new construction.
Get some one there who could tell if you would have a problem if you just drew in basement air for exhaust. Then you could leave the supply hooked up to the return duct.
You need to make sure that the exhaust intake will not cause problems like down drafting a water heater, or being too close to a furnace without a direct combustion air intake.
That could give you a steady supply of fresh air in winter without overdrying the house.
Or if you leave the ducting as is, just get a contractor who knows how to use relays and can read the manual that came with the ERV and the furnace.
On a rise in humidty, the ERV and the furnace fan run. Someone with a little control wiring skill could also have the ERV run whenever the furnace fired. Should get lots of ventilation air by operating it intermittently.
10-31-2005, 11:03 AM #5
Although not a very good investment in a mild climate, after paying for and installing an ERV, keep it! Optimum operation is a good discussion. After selling +1,000 HRVs most in WI, here is my opinion. Homes have the most natural ventilation during cold windy weather. Fresh air ventilation declines as the weather warms and winds decline. Mechanical ventilation is most needed to purge pollutants and replace oxygen during mild weather. If the home is always occupied, operate the unit at the speed needed continuously. If the home is occupied on a schedule like school and work during the week, a 2 hour weekly, repeatable interval timer operates on a occupancy schedule. Using a dehumdistat as a control requires daily reset to get the ideal indoor humidity for the variable weather. A humidistat is ok for a low limit control but doesn't get daily fresh air when needed.
Regarding fan operation, variable speed fan "on" slow is ideal with ERV except during a/c. On regular air handle fans, reduct the HRV to avoid fan operation during ventilation. Like exhausting air from the furnace cold air return through the ERV to the outside. Route the fresh air from outside ERV into a unheated basement area, as most fresh air works through the home from low to high. Always monitor the %RH in the home. Maintain <50%RH throughout the home including basement during the summer. Dehumidification is required in green grass climates. Avoid condensation on cold surfaces. Turn off fresh air ventilation with static electricity. Humidification may be required in very leaky homes during winter to avoid static. TB
10-31-2005, 11:57 AM #6
I used to advise customers to turn the dehumidistat down to 35% when it was below freezing, worked pretty good.
If they were still getting condensation they would lower it.
It really depends on how good the windows are, can maintain a higher RH in cold weather with good windows.
10-31-2005, 05:31 PM #7Regular Guest
- Join Date
- Feb 2005
Here is the ideal setup. The fan Tech exhaust fan should exhaust through the ERV.
The ERV should have a dedicated duct system. The reason is to be most effecient the ERV should draw air from areas of high humidity (kitchen and baths) and introduce air in occupied areas- family room, bedrooms, etc. When the furnace duct system is used the return air comes from about everywhere but the kitchen. This is not the air you want to expel all the time.
Secondly, with dedicated duct and controls, the ERV can run independant of the furnace. This will give you more control alternatives.
Thirdly, when an ERV uses the furnace duct system the relatively large blower motor plus up to two blower motors in the ERV must run. Not very effecient.
Also, running the blower in the sumertime may have adverse effects on humidity control when the A/C is not running.
I know it may be too late to make these changes, if not I would give this some serious consideration.