Tag Archives: ERV

Preliminary winter performance data

We have had temperature and humidity data recorded in the house over the last 4 months as part of a project conducted by Anthony Mach, a passive house designer and Building Science research student at Algonquin College. The preliminary data is now available, courtesy of Anthony. What we have here is essentially the raw temperature and humidity records in two locations: one in the middle of the open-plan downstairs space (1st Floor), and the other upstairs on the landing (2nd Floor). There is a lot of analysis to be done with this data combined with other data on external temperatures, energy use and so on.

A few things to note when looking at these charts:

  1. We were only half-moved in for most of November – we started using the kitchen sometime in the second week.
  2. When we moved in (around the 21st November), the HRV (which actually turned out to have an ERV core – for more on the differences, see here) had still not been properly balanced and we were still only using the system on its lowest setting.
  3. After the HRV had been balanced properly on the 4th December, we started using it on the middle setting, with boosts after baths and during cooking.
  4. We only had the 2kW Thermolec heating element, that works with the HRV, installed on December 14th. Up until that point we had only been using a single 1kW space heater. If it was cloudy in the morning after this point we used both, but if it was sunny we didn’t need the later.
  5. However, that installation coincided with a serious cold spell where external temperatures dropped to -25ºC or lower.
  6. We were away from the 20th to the 30th of December, and had the HRV just ticking over, which means that the house would have had almost no internal heating. You can see the drop, but what’s remarkable is that the place still never got below 13ºC.
  7. Once everything was back to normal and functioning properly, from early January, the temperatures in the house were generally between 17ºC (average night-time low) and 19ºC (average day time high) upstairs, with the extremes being 15.5ºC and 21ºC; and 18ºC (average night-time low) and 20.5ºC (average day time high) upstairs, with extremes of 16.5ºC and 22ºC. The difference is probably explained by a combination of the use of the extra heating downstairs, the passive solar effect from the larger windows, and generally that there is more activity downstairs for more of the time.
  8. The humidity has generally been where you’d want it, between 40 and 50%, gradually drying out as winter goes on. Our HRV having an ERV core helps in stopping the place getting too dry.

“The most airtight building in Ontario”

On Saturday, our advisor and supplier, Malcolm Isaacs from the Canadian Passive House Institute, visited us again to carry out the second (and hopefully, final) blower door test on airtightness, and to do some final tweaks to the Heat Recovery Ventilation (HRV) system to make sure it is fully balanced.

On the latter issue, we discovered one curious thing: our ‘HRV’ actually appears to have an Energy Recovery Ventilation (ERV) core. This means it actually not only uses a heat exchanger to transfer heat from the outgoing care to the incoming air, thereby keeping the air in the house both warm and fresh, but also balances the humidity (for more on the differences, see this Ecohome.net article). This is interesting not least because we only paid for an HRV, so far as we know…

However, the big news is something much bigger. When Malcolm last visited to do our preliminary blower door test at the end of September, various things weren’t ready, in particular, we had a malfunctioning and only partly sealed Motura sliding door, and the equipment wasn’t able to accurately record the figures we needed so we could only get a rough result. Even then we got a pretty good indication that the house was already well inside the Passive House standard. In the meantime, the door had been properly sealed, and Malcolm had obtained the component that would allow for the test to be done more accurately.

As the house was being pressurized, we went around with a little camera that measures temperature differences, to check for air leaks. We also discovered that one of the HRV ducts that goes through the outside wall was not actually as sealed as it should have been, despite the gaps between it and the wall having been filled with sprayfoam. So we had to seal up the edges with some more of that expensive but very effective Siga tape.

The process of doing a blower door test is outlined in the blog entry about Malcolm’s previous visit. You need only recall that you pressurize the house to 50 Pascals, and then record the amount of air that has to be added to the house to maintain that pressure. From these numbers, with the house volume, you can calculate the Air Changes per Hour, or ach50. The highest Canadian Standard, R-2000, is 2. The Passive House standard is 0.6. Last time we’d measured just above 0.4.

Malcolm did his measurements and then went away to do the calculations back home. From here I’ll just quote directly from his e-mail to us today:

“I’ve just finished recalculating the blower door test results from my visit yesterday. We did not do too badly, with an overall n50 airtightness of 0.185 ACH @ 50 Pa for both overpressure and underpressure. To the best of my knowledge this house is the most airtight building in Ontario […] This result shows the high quality and performance of all components used in the house, as well as the significant extra efforts of each of us who worked on the airsealing. The impact on overall energy demand in PHPP [the software used for calculating Passive House performance] is very significant: it drops overall specific energy use from 14.6 kWh/m2y (assuming 0.6 ACH)  to 12.5 kWh/m2y.”

For those of you who don’t speak Passive House, Malcolm provided a summary:

“Speaking as an engineer, we have a special technical term for this result: KICKASS.”

Quite. 🙂

Heat Recovery Ventilation 1

While slightly less got done in the house while we were away than we would have liked, the Heat Recovery Ventilation (HRV) system installation is now proceeding quickly.

Along with the thick insulation and sealed building shell, the HRV is one of the most important features of any Passive House. An HRV system is really very simple. In essence, it is a ventilation system with a heat exchanger, so that in winter, when cold air is drawn into the house, it is warmed with the heat from the stale outgoing air (and vice-versa in summer). However, it is also more than this.  The HRV ensures a uniform temperature throughout the house, taking the air heated by the sun through the large south-facing windows and distributing it to other rooms.

Our systems is also a little bit more than this. With the addition of a very small thermostat-controlled heating element (about the power of a toaster), it also becomes a low pressure forced air heating system. This will be the only artificial heat in the house, and we don’t think we’ll need it that much even in Ontario winters.

It’s worth noting that not all HRVs are created equal. Most of the manufacturers make claims about their efficiency,  but few of these are actually independently tested and verified, and this includes the leading companies in North America. This doesn’t mean they are bad, but you can do so much better. Our HRV is the ComfoAir 200 system from Swiss company, Zehnder, which is pretty much the best manufacturer of HRVs in the world. Their real tested efficiency is the highest, their systems are the quietest and their ribbed plastic Comfo-Tube ducting is much better than the old square section metal ducting you might be used to. Our system was supplied, with minimal fuss, by the excellent Hans, from Zehnder’s Ontario dealer, Pinwheel Building Supplies.

You need to plan for the installation properly from the beginning though. We didn’t but we got lucky. The units themself take up a fair bit of room. However they can be mounted on walls or ceilings. Since we have massively over-engineered CLT ceilings, we did the latter, mounting them up, out of the way, in our machine room, which just happens to have enough room up there. There are a lot of ducts too – intake and exhausts in different parts of the house – and the ducting goes up through what would have been our chimney openings. Again, this was luck rather than judgment. We also didn’t get the design for the HRV system ducting done before we ordered the CLT, so rather than having pre-drilled fittings, the builders are having to drill through the thick ceilings to make the vent holes.