Does anybody know of ERV's or HRV's that sense negative indoor air pressure caused by exhaust systems and balance the negative pressure by allowing additional air in?

I don't, but a large barometric relief damper would prevent negative pressure from getting too extreme. And since you don't have the reverse airflow available (it's going out the exhaust fan), I don't think that doing it in an HRV would save energy anyway. But it would be nice if residential HRVs could actively control building pressure - there are good reasons (humidity, pollution, wall moisture) to maintain a slightly negative or positive interior pressure.

The manufacturers of HRV and ERV equipment advocate balance and will not discuss makeup air for any appliance. The units are designed to recover energy while exhausting foul air and replacing it with fresh outdoor air.

If you wanted to maintain exact balance, you could install two fans in a push/pull configuration and wire them to the same switch. Or use the HRV return as the exhaust. But that doesn't help if the cause of the exhaust is the clothes dryer.

Typically, you don’t want to create positive pressure in a building (i.e., the supply only fan method of ventilation) because this may force inside humid air into the building assemblies. Typically, you also don’t want to create negative pressure in a building (i.e., the exhaust only fan method of ventilation) because this may force outside humid air into the building assemblies and may also increase the risk of back drafting from combustion appliances. So typically, for maximum cooling/heating efficiency, you want to maintain equal air pressure. This means the exhaust and the fresh air rates are about the same. So I believe the question being asked here is how best to address the requirements associated with combustion air (e.g., appliances needing combustion air) and makeup air (e.g., appliances such as stove exhaust fans needing makeup air) when you are also using a HRV to meet your basic ventilation requirements.

In full-time residential building ventilation applications, HRVs are generally setup in a neutral, equal pressure scheme to provide your ventilation air. However, in part-time commercial building ventilation applications, HRVs are sometimes intentionally run out of balance to achieve a preferred pressurization scheme. In commercial buildings you could have the exhaust air rate exceed the fresh air rate by about 10% to create a slight negative pressure in the winter. In the summer, you could have the fresh air rate exceed the exhaust air rate by 10% to create a slight positive pressure. These preferential pressurizations are intended to control which way air will flow through the commercial building envelope at different times of the year. In the winter it is often better to encourage dry winter air to pass in through the building envelope as it will not condense on its way in. In the summer, it is often better to encourage dry room air to pass out through the building envelope as it will not condense on its way out. I only mention this because there are actually people in the HVAC industry that know what they are doing and this scheme can also be used to good advantage in energy efficient residential building applications too.

So with the HRV basics out of the way, you first need to make absolutely sure that your combustion appliances have the required amount of combustion air. In my opinion, just directly venting these appliances is the best way to address this for a residential building. To address large exhaust appliances such as a stove exhaust fan, you will most likely need makeup air at a higher rate than your HRV will be capable of supplying. This is typically accomplished with a local dedicated makeup air fan, sometimes even with a means to temper the makeup air temp (e.g., electric duct heater). This makeup air fan can be wired to operate at the appropriate rate and temp when the large exhaust appliance is operating.

We need to do a sticky on this subject which deals with the various types and volumes of makeup air which might be required in an appropriately tight home. At one end of the scale is gargantuan range hoods moving 1200 CFM which are WAY out of the capabilities of any HRV to deal with, down to the more reasonable ones like bathroom exhaust fans.

Does anybody know of ERV's or HRV's that sense negative indoor air pressure caused by exhaust systems and balance the negative pressure by allowing additional air in?

There are a lot of things which might cause interior pressure differentials and the HRV/ERVs have a limited ability to compensate. I have an Ultimate Air RecoupAerator 200DX. It has an optional air pressure sensing unit which can control the HRV. Keep in mind that the total capacity of this system ( and it's a large one) is 190 cfm, which can do nearly nothing when the 1200 cfm range hood goes on.

Nice, it looks like the pressure control option for the 200DX allows it to maintain (or attempt to maintain) 0, 1 or 2.5 pascals above outside pressure. If you wanted a slightly negative pressure (as you might in cold weather for wall moisture reasons), I suppose you could reverse the connections.

There was an article on GBA that talked about range vent hoods and ventilation. It mentioned that some 1,000 cfm + range hoods in tight homes will create a back draft and there has been cases where it can become dangerous with fireplaces and gas appliances.

It seems kind of counterproductive to build a super tight home and then throw in a 1,000cfm + range hood. One would have to open a window to equalize the pressure in the home when running one of those beasts. 

I suppose you could reverse the connections

Yes, you can choose both the interior state, positive or negative and the sensitivity of the unit's response.

I do have to warn you that even the nerd HVAC guy's eyes glazed over when he saw it in the "TO DO" bin.

It seems kind of counterproductive to build a super tight home and then throw in a 1,000cfm + range hood.

No question there. But, if you want to live out your golden years cooking with gas blowtorches, you don't have much option. In a mild climate, with a very large home to buffer the changes, it's not too much of a real problem. If you had a modest little home with a fancy kitchen in an extremely cold climate, things wouldn't be so workable.

ETA: I have large 4' X 2' sky lights directly adjacent to the range hood that can open when the hood is ON, sending a cascade of outside air down to get sucked up.

Yes, like the 200DX, there are some HRVs that will attempt to maintain a pressure differential set point to the limited extent that they can given their limited flow rate. There are also “smart” fans that can be controlled to turn on/off when other “smart” fans are turned on/off. For example, Broan’s Smartsense Intelligent Ventilation System:

http://www.broan.com/common/productDigitalAssethandler.ashx?id=0104c28c-2899-4fcd-83c8-d6c434018003

So you don’t actually have to physically hard wire your exhaust and makeup air fans together, but often times maintaining HVAC system simplicity is the best policy when all is said and done. Sensors and automation can fail and not all home owners have the right stuff to know when this has occurred or how serious the failure could be to their well-being. The good news here is that makeup air is only typically required for a very small percentage of the time.

Makeup air units are typically mandated for hoods exceeding 600 cfm and all of the fans mentioned are incidental loads. Pulling a negative for 20 minute or even an hour of cooking or showering will not hurt anyone. If you have open combustion you would need combustion air full time.

According to this, as little as 200 cfm of exhaust can create problems (like carbon monoxide) for some devices in a tight house. And makeup air via a non-fan-powered intake duct is surprisingly ineffective. So where are the house pressure sensing, variable speed, powered intake systems that can move up to 1000 cfm (as the OP seems to want)?

I would highly recommend Paul Raymer’s Residential Ventilation Handbook to gain a basic understanding of ventilation principles. Paul is an ASHRAE voting member of the 62.2 SSPC. You can purchase intake/exhaust fans to provide the required CFM flow rates. You don’t need a complicated pressure sensing control system to accomplish this mission. You do need to be competent in HVAC system design/installation.

I second the above recommendation to read Paul Raymer's book. I know this will make some cring, but I plan to someday install a 1200 CFM range hood and I've done a lot of research on the subject. Utilizing an ERV for make up are doesn't seem possible. My current idea is to install two makeup air vents (with some sort of decorative trim) in the wall behind the stove just above the cooking surface. These vents would incorporate automatic damper controls similar to the Wolf Automatic Make-up Damper with Transformer & Pressure Switch. (I tried to upload the PDF but it is too big for the site.)

How big will these vents be and what's the worse case (accounting for other devices that also exhaust air) negative pressure limit you will achieve?

Posted By jonr on 12 Jun 2014 09:32 AM
How big will these vents be and what's the worse case (accounting for other devices that also exhaust air) negative pressure limit you will achieve?

On my attempt to solve this problem, my make up opening will try to match the output vent opening.  My hood openings are square, but my make-up air openings are rectangular based on the damper that the hvac guy plans to use.

I think that if you do the calculations (and I understand your situation correctly), you will find this inadequate. A duct with a fan is not balanced by a similarly sized duct without a fan.

On the other hand, if you have CO detectors, as MA says, 20 min of negative pressure now and then might not matter.

I guess I should check the sizes exactly.  Hopefully, it isn't too undersized, or else, we will have to open windows.