A better way to control your HRV

The goal of this little project is to minimize BTU loss and electricity use (the costs of running an HRV), while ensuring good air quality in our work environment.

I've been on an efficiency kick in our 9100 sq/ft headquarters, building on a net zero goal envelope update completed 3 yrs ago. Having recently updated the building's 9 thermostats to Ecobee3 units, the next step is HRV control. The building uses a Venmar 220V commercial unit for fresh air exchange. It was previously just controlled by one of the air handler fan circuits, so operated via the thermostat's programmed fan function. This method of operation is pretty much a guess at adequate ventilation, and may in fact be quite wasteful.

We're trying to keep the building as simple as possible, so have deliberately avoided a dedicated building control. The Ecobee3 thermostat can control an HRV using an standard set of dry contacts. This however only runs the HRV on a schedule, rather than on demand.

Based on some research, particularly as humidity is not an issue, controlling the HRV based on CO2 levels makes a lot more sense. Here are some baselines. "ppm" means parts per million as a measure of C02 levels in air. From kane.co.uk:

250-350ppm Normal background concentration in outdoor ambient air
350-1,000ppm Concentrations typical of occupied indoor spaces with good air exchange
1,000-2,000ppm Complaints of drowsiness and poor air.
2,000-5,000 ppm Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.
5,000 Workplace exposure limit (as 8-hour TWA) in most jurisdictions.
>40,000 ppm Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma, even death.

A call to Co2meters.com resulted in a few recommendations to manage our HRV. Joshua knew exactly what I needed, and was extremely knowledgeable. I ordered up the RAD-0301 Indoor air quality monitor, as well as the TON-0007 Co2 Monitor with Relay

The Co2 monitor plugs into a computer or power supply via USB, and uses free software to log levels. The wall mount CO2 monitor runs on 24V (like the HVAC system) and has a relay that in our case will open at 900ppm, and close when levels fall below 700ppm. You have four options, 800ppm, 1000, 1200 and 1400 set by jumpers for relay control.

You can see here that C02 levels in my office are just under 700ppm, with the HRV running constantly for a few hrs. The unit on the right is the USB powered monitor, and on the left, the wall mount monitor that will eventually control the HRV.



Before I install the wall mount units, wired to the HRV, we'll monitor a bit to see what our baseline looks like. The small monitoring unit plugs into a PC USB for both power, and the ablity to log CO2 levels.



I'll update this post as we move through the installation.

Dennis, this is a very interesting post. I assume you also have mechanical A/C to control humidity and temp in the summer? CO2 monitoring is a good control strategy, especially if personnel levels are not fairly constant. Is the Venmar ducted into the air handlers or is a stand alone system? Was the building balanced after installation? Where will you place the monitor or can you get multiple sensors for a more accurate picture of what is going on?

Codes around here dictate system design based on air changes per hour, not CO2 levels,ect.An HRV system is sized on CFM requirements for the proper number of air changes and then simply runs on an occupied/unoccupied cycle.Of course you can add any number of bells and whistles to such a system. Do you happen to know what the codes are up there in Canada?

Another thought popped in my head Depending on what you have for duct work, you may want to install a VFD with the appropriate motor and controls to vary the CFM of the Venmar.

Mr onetwo said:

Dennis, this is a very interesting post. I assume you also have mechanical A/C to control humidity and temp in the summer? CO2 monitoring is a good control strategy, especially if personnel levels are not fairly constant. Is the Venmar ducted into the air handlers or is a stand alone system? Was the building balanced after installation? Where will you place the monitor or can you get multiple sensors for a more accurate picture of what is going on?

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Mrone, those are great questions. Our building has five air handlers for both fresh air and cooling. All five of them also have a heat coil, and the three upper floor handlers do heat. On the main floor we have two air handlers, but also four zone radiant across 4800 sq/ft. Heat on the main floor can be done with the air handlers, or the radiant floor. This was an over-pour + insulate over the existing slab.





The fifth air handler for our film studio has it's own Lifebreath HRV, and is acoustically isolated from the other four.

The larger Venmar HRV services four air handlers ducting fresh air into each of their returns. The entire system is balanced as per code here for fresh air requirements. I don't know the precise CFM/occupant requirements, however I can get them from Todd Lowey, the engineer here who designed the system. He's an awesome guy.

You are exactly right with the varying personnel comment. It varies from 20 to zero on the weekends. I have two wall mount C02 units, so for sure one will go on the wall, about 4ft up between the two main floor air handler intakes. I'm going to log C02 levels for a few days to get a good sense of where it makes the most sense for the wall mount unit.

One of the items that made no sense to me after the initial install is that when the HRV is running, ideally the air handlers should also be in fan mode to circulate the air. We could leave everything running, all the time, but that would be wasteful of both power and BTUs. The nice thing about the ecobee3 stats is that they are easy to integrate with automation. Right now, the fans only run on the air Handlers when the ecobee3 stats or sensors detect occupancy in their respective zones.

When the HRV install is complete, I'll likely have a simple zwave relay communicate the HRV status to the Ecobee3 stats. This should play well with the night-time cooling strategy for the building as the HRV will pull in cold air via a bypass, and the air handlers will circulate the cool air to pre-cool the building.

We also have a clerestory with stand alone solar powered openers ( http://solarsmartopener.com/ ) , a fantastic product. This system opens the clerestory windows on summer nights (when interior temps climb above the programmed set point) to assist with night cooling. All of this will play into the summer cooling strategy..but that's another post

Co2meters does sell monitors that I believe you would use with a full building control system as they have 4-20mA or 0-10VDC outputs that could stage ventilation as C02 levels rise. The Venmar is a very efficient unit, but only has two speeds, controlled by dry contacts. I've always found the lower speed works well, and the first day of C02 logging confirms that. The Tongdy is relatively inexpensive, and provides exactly what I need..a closed dry contact relay which opens at 900ppm, and closes at 700ppm.

I have two of these:



Nelson at CO2meter.com suggested 700 is a very good target for air quality.

It is always a balance between efficiency and comfort. I have found that people complain more in a building that does not have constant circulation of air with the proper percentage and mixing of fresh air during the occupied mode. Without air movement, the building air "feels" dead. Perhaps you should do an electrical study to see how much electricity your AHU's actually use in a 24 hour cycle. Then you can calculate how much you can save during the occupied cycle cycling on & off per CO2 levels.You may be surprised at how little it actually is. Another factor is motors don't like to cycle on and off...they last much longer when run times are longer.What is your current control schedule for the AHU/HRV system and how does it tie into the infloor heat?

Mr_one, interesting that you would ask about consumption Last weekend showed lower consumption than we've ever seen due to the Ecobee3 install and some pretty aggressive set backs. The only difference was decreased (or zero) run times on the AHU units, the Triangle tube boilers (there are two, swapping heating chores every day) and circulation pumps. The HRV units normally don't run on the weekends.



One thing I've noticed over the last day is that with higher winds outside (20-30km/h) the CO2 levels in my home for example have dropped from 1100ppm to around 700ppm, with all windows closed. The office was as low as 500ppm on Sunday (with no one there).

The in-floor heat has zero tie in to the AHU units, however I have the mainfloor AHU units running in low speed fan mode when the Ecobee3 stats detect occupancy..so the fans will stay on as long as my team is present. I've never liked the HRV cycling with the AHU fan program (20 minutes/hour) for exactly the reason you stated..cycle times and electrical failure. Running it off the CO2 control (turns on at 900ppm, off below 700ppm) should decrease cycle times and run the HRV only when needed.

My expectation is that on days like today with higher winds outside, the HRV might not run at all, even in our relatively tight building, due to natural "ventilation". Conversely, the Co2 control may run the HRV all day if outside winds are zero, it's warm (reduced stack effect) outside, and we have a larger team working.

Once we're done the little project, the data should be a useful reference for anyone looking to replicate the process Thanks again for your comments..they are good motivation to keep posting up data.

Wind pressure is a factor...no building is 100% tight, unless it is buried I suppose.Once you are up and running via CO2 I would monitor run times on the HRV to make sure you are not short cycling it. In the main area, which heat source is primary...infloor or AHU?Is it offices or a common area? What percentage of this area is entrance? Too many questions!I'm glad you find my "ruminations" useful. This is a very interesting discussion for me.Hopefully it will be useful to someone else.

Actually they are very good questions. The engineers who design and spec systems like ours don't necessarily focus on efficiency as code dictates CFM rates as a minimum. Running a constantly running primary loop for example in a building like ours is very wasteful.

I've been experimenting a bit (since the Ecobee stats are data logging) with a 3 degree set back on radiant. Rather than sinking BTUs into the slab in the main work area (which tends to warm up past set points during the work day), I've been setting the radiant it to recover to 19C, and have the main floor AHU units take the room to 20C for the work day. This way the slightly cooler slab seems to control the extra heat from human activity.

The radiant is four zones. Two front entry ways and air isolated workshop are covered by zone 1. This zone is currently run at 10C, and a remote sensor in the entry vestibule ensures the primary entry never freezes. Zone 2 is our loading bay, kept at 8C. There is a 14ft overhead door there, so the 16x32 loading area is insulated additionally on inner walls to mitigate heat loss. Zone 3 is the main work area (office, assembly, shipping) set to 20C so also serviced by two AHUs for fresh air/cooling. Zone 4 is a rear entry area, again using a remote sensor to hold it at 10C. The cool entry areas are isolated with fire doors, so lockers and boot trays etc are on the warm side of the areas.

I have all the equipment data logging via the Ecobee web portal, so can post up any plots if you're interested in specific behavior.

My thinking based on logging so far is that the 200ppm window on the wall control (on at 900ppm, off at 700ppm) should prevent short cycling. Will definitely monitor.

I agree that a 200PPM offset will probably take care of short cycling. You have a good handle on things and hopefully you will be satisfied with the end results...it will take 12 months for a complete picture to develop. Maybe someday I can come visit.

It's a long drive, but the coffee is always on..and the beer fridge stocked

Here's a few C02 level plots done in the 2-4pm range by one of my crew. On Monday, the HRV was run on a manual schedule from 6am to 7am (off peak hydro), then again from 1pm to 3pm. On the weekend, the HRV does not run at all as normally there is no staff working.

Based on these plots, I would guess running the HRV based on actual C02 levels will not run much with winds 15km/h and above outside, forcing air through the envelope.

Mr_one, all of the offices have opening windows, but at -34C on one is opening them! You raise a good point though. One of my automation goals is to have an open window "event" shut down AC and HRV for that area for the summer months.

The offices all have both supply and return air, so technically we don't need opening windows. The building was designed for passive convective cooling, and I encourage it. The only issue is managing the AC. I just ordered a few Smarthings automation hubs, so will use these to manage the whole night cooling and AC issue. We have a security system that can be integrated to automation. This way I can use the existing window sensors to trigger events (like turn off the AC) on window opening.

What's the airflow balance on the HRV(s)? I assume you're running slightly positive?

At least you will get some fresh air in all the offices at elevated wind speeds. Do you plan to run the HRV and fans when the outside temp drops below a certain temp at night to exhaust heat buildup from the day? I like the window opening idea...very clever.

Yes..in about 2 months the heating system will be off, and cooling will be an issue. If the outside temps stay below 16C (60F), we can cool passively if windows are opened.

When temps climb up over 20C then AC is required. Pre-cooling the building at night to say 18C means AC won't kick in until 1pm or so. The Ecobee stats can trigger free cooling by themselves if you wire the HRV to them. The end result will be a system where HRV can pump in cool air using a bypass, and the air handlers can distribute this to all areas of the building.

Denwood said:

Yes..in about 2 months the heating system will be off, and cooling will be an issue. If the outside temps stay below 16C (60F), we can cool passively if windows are opened.

When temps climb up over 20C then AC is required. Pre-cooling the building at night to say 18C means AC won't kick in until 1pm or so. The Ecobee stats can trigger free cooling by themselves if you wire the HRV to them. The end result will be a system where HRV can pump in cool air using a bypass, and the air handlers can distribute this to all areas of the building.

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This is exactly what you want to do....when you hit 18C overnight just kill the whole system. Every minute you don't have to use mechanical cooling is money in the bank!What brand of air handlers did you use in your building?

The air handlers are ADP, B series: http://www.adpnow.com/wp-content/uploads/2010/10/SG-BAH-17.pdf

They have high efficiency variable speed ECM motors with quite a few jumpered CFM options on the mainboard for fan speed, cooling and heat modes.

I did a quick plot at my retrofitted 100 yr old home, which shows that we definitely need to add an HRV into the mix. Originally the home was blower tested at 3 full air changes per hour, however it's much tighter now. Levels at night with the four of us are in the 1200 ppm range. An HRV is required. The work location conversely is running at half these levels if you check the plots previous in this post..but also using proper ventilation.

Fyi, I think the original link is a bit conservative on the CO2 concentrations. Check out ASHRAE technical FAQ ID 35.

Also, have you done any cost analysis of providing an HRV for your home vs. ducting a small amount of ventilation air directly do your central HVAC unit?

Pseudo, thanks for that reference: https://www.ashrae.org/File Library/docLib/Technology/FAQs2014/TC-04-03-FAQ-35.pdf

It's interesting that 700ppm more or less corroborates 15cfm/person at the office. That's likely what code dictates. That reference also indicates 1000ppm might be ok. My wife definitely is pushing for better ventilation.

I've been doing a bit of research on the home ventilation issue. I found this very cool product from Panasonic: FV-04VE1 WhisperComfort Spot ERV: http://www.amazon.ca/dp/B000XJNZ1Y/?tag=atomicindus04-20

It's an ERV at 40 CFM, 23 watts that would fit into a ceiling. It's an ERV, so no condensate drain is required. It looked perfect until I read the manual online and saw that below -7C it switches to exhaust only. This would have been perfect to replace our bath fan as our three bedrooms are on the same floor.

I'm leaning towards something like the Zehnder Comfoair 160 or 200 ventilation unit rated at 92% efficiency with summer cooling bypass. http://zehnderamerica.com/products/heat-and-energy-recovery-ventilation-units/. Based on ASHRAE 62.2, (7.5 CFM per person + 1 CFM / 100 sq of living space) I should be looking to around 60 CFM as a baseline.

Some further HRV/ERV options for older homes, or folks looking for other options than a full blown HRV install.

The Panasonic FV-04VE1 still looks like a great option, but warming intake air when temps fall below -7C would be required to keep it operating in ERV mode. Very affordable at $357..and capable of 40CFM:



I also found a new product, the Luna e2 which is very interesting...and has a US distributor. You install them in pairs, and the controller alternates fan direction every 70 seconds. A ceramic core in each 6" fan assembly manages heat recovery. One fan warms it's core in exhaust mode, while the other recovers heat from it's core in intake mode. Then they swap. They are not cheap...$1000/pair rated at 22CFM. I'd need two pairs at least. This system does look to be very efficient.



They also have a spot HRV rated at about 11cfm which combines the fans into one unit. These fans likely reverse in cycles as well, so you take a hit on air flow. Not a bad idea for a bathroom.



The Panasonic ERV unit fits into a 16" stud space, uses only 23 watts at 40cfm, is nearly silent, and requires no condensate drain. In terms of price/performance, it looks hard to beat. Our temps in winter fall below -7C frequently, so warming intake air (or just settling for exhaust mode under those conditions) would take some work. There are some simple solar space heating designs out there which would warm intake air, at least when the sun was shining.

To wrap up this thread, here's the final install. Power to the CO2 meter is running from a 24volt transformer that was already in place in our mechanical room. The dry contacts to the HRV (on the 2nd floor in another mechanical room) are routed using two of the eight wires in an unused CAT5 network cable. The building network patch panel is very close to the HRV, so this was an easy way to connect to the Venmar HRV.

pseudorealityx said:

What's the airflow balance on the HRV(s)? I assume you're running slightly positive?

Click to expand...

Pseudo, sorry I had missed your question. I believe the bias currently is positive. That said, we have a work room which has a 1600 CFM exhaust fan which brings the entire building negative so any dust/fumes etc are isolated. This same fan has proved effective to speed night cooling. The work room has an automated makeup air vent which draws exhaust air at about 800 CFM from conditioned air.

The folks over at Co2meter.com evidently liked this thread

http://www.co2meter.com/blogs/news/128721927-co2-meter-helps-lower-heating-costs-for-business

Hi Dennis,

Very interesting stuff, thanks for posting!


I don't currently need to worry about ventilation in our 1975 house; the leaky window seals take care of it quite nicely, but some day I hope to seal it up well enough that an ERV is required. I appreciate the detail you put into your posts, including real data showing the results!

Just updating broken pic links and realized I missed your reply Pressing. In case anyone is wondering the Panasonic ERV is more or less running 24/7 and zero issues since installation.