December 12, 2018

My start in the industry happened to coincide with the early days of the R-2000 Housing program. That program was the result of millions of dollars of Canadian research that demonstrated how to optimize energy performance in cold weather housing. The research, and the R-2000 program that came out of it in 1982, drove the early development of HRVs, insulated sheathing and window glazing options. I recall the passion and enthusiasm of the builders, energy professionals and manufacturers who participated in those early days. I am intrigued to see a similar passion and enthusiasm exhibited by proponents of the Passive House program that has been introduced to North America over the last decade or so.

vanEE Gold Series 2400E ECM

PASSIVE HOUSE PROGRAM HISTORY

Originating in Germany in the late 1980's and building on the earlier Canadian research and experience, the Passive House program is perhaps the most rigorous energy-efficiency standard in the building industry today. Indeed, one of the underlying objectives of the standard is to build enclosures efficiently enough to avoid the need for conventional heating and cooling systems. This is not to say that HVAC contractors and manufacturers need to be worried that they won't get a call to provide goods or services in Passive Houses. It does mean you will have to be respectful of the nature of the loads in a Passive House building (the Passive House concept is of interest to architects in commercial, institutional and residential projects) and be flexible in your approach to meeting the total indoor environmental control and comfort of occupants.

MODELLING THE ENERGY

Much like the R-2000 program, Passive House has its own proprietary energy simulation software and energy targets based on that energy model. The results won't necessarily give you the same results as say a simulation done using Natural Resources Canada's HOT 2000 Energy Simulation software or, perhaps more importantly, outputs from common heat loss and heat gain that are compliant with the CSA F280 CAN/CSA F280-12 Standard Determining the Required Capacity of Residential Space Heating and Cooling Appliances. However, the software is recognized by the Ontario Building Code and the British Columbia Building Code for determining energy code compliance.

MECHANICAL TARGETS

The important part of the program for mechanical professionals is to get comfortable with the Passive House performance metrics or requirements. There is, of course, a comprehensive list of the enclosure and mechanical requirements for a Passive House building, but the primary requirements of interest to mechanical contractors are as follows:

• An instantaneous Heating load of no more than 10 Watts / m2 of usable floor space OR
• The Annual Space Heat Demand must be no more than 15 kWh / m2 of usable floor space.
• If cooling (air conditioning) is required, the annual cooling energy demand must also not exceed 15 kWh / m2.

Let's consider an example, using my own 2,100 ft2 Net Zero Energy home. The definition of usable floor space within Passive Houses has its own nuances, but for the purpose of this example, let's assume all 2100 ft2 or 195 m2 is usable. That would mean, the heat loss for the building could be no more than 1950 watts. That's just a heat loss of approximately 6150 BTUs/hr in imperial units. Moreover, in the Passive House program, there is no allowance for climate zones, so this heat loss compliance would be the same for Vancouver to Edmonton to Windsor to Quebec City to Halifax.

The alternate compliance metric would be the annual space heating demand. In the example house, that metric would allow a maximum of 15 x 195 = 2925 kWh of energy used for space heating. Fortunately, the Passive House software considers solar gain and, to some extent, thermal mass, such that it encourages large expanses of south-facing glass to get as much "free heat" as possible. The table below shows the results from the Passive House software for that 2100 sq.ft. houses under 2 scenarios; as it was designed to meet Net Zero specifications and what Passive House ultimately recommended to meet their requirements.

A QUICK COMPARISON OF NET ZERO VS PASSIVE HOUSE SPECIFICATIONS

There are a number of interesting elements to this comparison. Notice that the design cooling load for the Passive House went up. In order to meet the annual space heating load, the Passive House software recommended increasing the amount of south-facing glass by over 160 sq.ft - triple what was originally in the design. Then, Passive House software, in my opinion, underestimates cooling loads significantly. First, it assumes a set point temperature of 25 0C (77 0F), rather than the Canadian norm of 23 0C or 24 0C (74 0F to 75 0F). Second, for those readers who do heat gain calculations, you will recognize that the base 4,000 BTUs/hr cooling load would just barely match the appliance and people loads in a CSA F280 calculation. Passive House makes different assumptions about people, appliance and hot water loads than we traditional use in Canada. However, Passive House software does calculate the percentage of summer hours that a house or building will be above the set point temperature of 25 0C (77 0F) and limits that percentage to less than 10%. In the example above, those calculations indicate the house will be above this temperature 27% of the time. Rather than recommending additional cooling, however, the Passive House consultant recommended extra southern face shading and a night-time by-pass of the energy recovery core or whole house fan. This may not be practical in the parts of Canada that have high night-time humidity levels.

GOING COMPACT IN DESIGN

With such an aggressive energy target based on usable square footage, Passive House design is sensitive to window areas to maximize potential solar gain. It is also sensitive to the "compactness ratio" of the design. My house was a relatively long, narrow rectangle due to lot limitations. This means a fairly high exterior surface area to usable floor area. In general, you will find Passive House architects trend to more compact, cubic configurations with large, south-facing windows that have high solar heat gain coefficients.

I should point out that the normal Passive House airtightness standard is 0.6 Air changes per hour at a pressure of 50 Pascal (ACH @50 Pa). However, in order to achieve the heat load demand and heat loss, the consultant recommended lowering the airtightness level to 0.2 ACH@50 Pa. Although I did not proceed with trying to meet the Passive House standard, I did ensure the house tightness was under that 0.2 ACH@50 Pa limit, just for bragging rights.

RETHINKING HEAT IN HOMES

The very modest heating requirements of a Passive House leads to a rethinking of heat distribution. In Europe, the base system is typically a fully ducted Energy Recovery Ventilator - exhaust from bathrooms and kitchen, fresh air to all other rooms. To deliver the 6,000 BTUs/hr or under 2 kW of heat in the example above, an air volume of just 150 to 200 CFM could be used. This is well within the capacity of the ERVs that are designed specifically for Passive House. In fact, the European models include an air source heat pump within the ERV. Unfortunately, there are just one or two of these units that meet the basic National and Provincial requirements for cold weather performance in Canada as outlined in the Home Ventilating Institute (HVI) test protocol. There are Canadian made ERVs with adequate airflow capacity and efficiencies above 90% Apparent Sensible Effectiveness suitable for Passive House where a simple duct heater could be added. The other rather obvious approach to Passive House heating and cooling would be the mini-split, variable refrigerant air source heat pumps that are now so common. A couple of small capacity wall mount heads or a mini-ducted version would provide all the heating and cooling required.

While Passive House continues to be a niche market, more popular in mild climates such as Vancouver, it has gained the attention of those architects looking towards the Net Zero goal for all buildings by 2030. Professional mechanical contractors will do well to recognize the passion and enthusiasm Passive House proponents have and put aside your own preconceived notions of how much insulation is enough or how to calculate payback. Passive House is a rigorous, well thought out program that allows you to provide exceptional comfort and air quality with small, premium performance equipment.

This ERV unit is Canadian made and meets Passive House expectations for high performance. It could provide adequate airflow to deliver the heating capacity needs of many Passive Houses.

This article was written by Gord Cooke, President Building Knowledge Canada and originally published in Mechanical Business, September 2018 edition.