Transsolar Designs a Mechanical System That Is a Breath of Fresh Air

In his book "The Architecture of the Well-tempered Environment" (our late review here), Reyner Banham noted that architects and designers had "abdicated their responsibility for indoor comfort, designing without consideration of the consequences for the indoor environment, and just handing the whole thing over to the engineers and contractors to solve it for them." The result, as I noted earlier, was that "today's mechanical engineers who design and build and operate HVAC systems in buildings large and small are isolated from the construct of the building as an integrated system."

That's certainly not the case in the Toronto Region Conservation Authority Building covered earlier on Treehugger. where the mechanical systems were integral to Bucholz McEvoy and Zas Architects' design of the building. It had a very interesting heating, ventilation, and cooling (HVAC) system developed by Integral Group and Transsolar, the innovative German firm that specializes in "user-centered design and access to natural light and air for improved occupant productivity" Krista Palen of Transsolar's New York office worked on the project and walked us through it.

One of the key features in the system that is common in Europe but unusual in North America is that ventilation, the fresh air required to keep Carbon Dioxide at safe levels, is separate from the heating and cooling required for comfort.

This is not how it is usually done in North America, where large volumes of air are heated, cooled, and recirculated, with a small percentage of fresh air added. This has become a problem in the aftermath of the pandemic, when office and commercial building owners are scrambling to crank up the ventilation rates, and are finding they need a lot more heating and cooling to temper all the fresh air that the system wasn't designed for.

In the TRCA building, the ventilation systems include operable windows, and a system where fresh air is drawn in through the glass chimneys described previously by project architect Peter Duckworth Pilkington as  "giant glass air ducts with MERV 13 filters on the top. Inside, there are steel mesh screens with water running down, filtered through reverse osmosis and UV, tempered by the ground water to be warm in winter, cool in summer."

The air is then distributed through the plenum underneath the raised floor after passing through a heat recovery ventilator (the red box next to the blue chimney.) Return air is picked up from the floor below, run through the HRV and exhausted to the roof. The amount of fresh air is determined by CO2 detectors.

Palen explains there are "three different operating modes: heating, cooling, and natural ventilation. In heating and cooling modes, air coming into the building is preconditioned by the water wall inside a glass duct, water coupled to the ground by geothermal wells. The geothermal system also provides hot and chilled water to the radiant ceiling, and to the air handling units with a ground source heat pump."

Heating and cooling are a separate system, delivered through radiant panels in the ceiling. This is counterintuitive in North America, where people say "that won't work, heat rises!" But heat does not rise, warm air does because it is less dense than cold air.

The point of heating and cooling is human comfort, about half of which comes from the air temperature, and about half from Mean Radiant Temperature (MRT). where heat radiates from warm to cool surfaces. So if your warm skin is near a cold wall, heat radiates from you to the wall and you feel cool. If you are sitting under a radiant ceiling that is warmer than your skin, then you feel warm.

MRT is not well understood but as Robert Bean of Healthy Heating notes, it is a very big deal, and changes the way you think about comfort. Bean writes: "I say, if building codes dropped the reference to controlling air temperatures and switched the requirements to controlling mean radiant temperature, building performance specifications would have to change overnight." It is the reason that buildings designed to the Passivhaus standard are so comfortable; the walls are as warm as the room. And it's why the TRCA building is comfortable, with its well insulated walls and windows.

To the extent that you can use natural ventilation in Toronto's humid summers and cold winters, the building occupants will get fresh air by opening their windows. According to Pilkington, "Under the right exterior conditions, staff will be alerted by the building’s automation system through their personal devices to either open or close windows, to ensure the building is using energy most efficiently."

Note how the operative air temperature varies far more widely than most people are used to in offices, from a low of 70 degrees to a high of 82 degress. We have noted before that most office thermostats and mechanical systems are set for the comfort of men in suits. Krista Palen says that now we have "a different mentality; we are used to overcooling, and women, who were too cold, now have a stronger voice." With climate-appropriate clothing such a temperature range is not uncomfortable.

This is obviously not your typical urban building on your typical urban site, with your typical mechanical system. But there are some basic principles that should apply to every building from now on in the aftermath of the pandemic:

Don't recirculate air, period. Have a heat recovery system and exhaust the inside air and bring in fresh outside air to the extent you need for appropriate CO2 levels. As Kristof Irwin wrote last year:

"Ventilation is crucial. Bringing in more filtered outdoor air in buildings heating/cooling systems (or opening windows in buildings that don’t) helps extract airborne contaminants from the building, making infection less likely. For years, we have been doing the opposite: sealing our windows shut and recirculating air. Just look at the residential code requirements for ventilation (or even scarier, look at the enforcement). The result are homes, schools, and office buildings that are chronically under ventilated. This not only gives a boost to disease transmission, including common scourges like the norovirus or the common flu, but can also significantly impair cognitive function [from high CO2 levels]"

Of course, just about every office building and home in North America has a recirculating air system, but that doesn't mean we should keep building them. This isn't new, it is common in Europe, and this is what the Passivhaus people have been saying for decades.

Why pay for cooling when you can get it for free? The TRCA building uses natural ventilation and lots of fresh air drawn in through those giant glass ducts, which are tempered by the free cooling of the wet wall. This is pretty elaborate, but in shoulder seasons there is lots of fresh air that is a reasonable temperature than can be pumped through any building.

Get used to a wider range of temperatures. This applies for any building; offices used to be kept between 70 and 73 F, and with such a narrow range, the cooling or the heating is always running. Accepting a seasonal range of 70° to 82° uses a lot less energy.

Heating, cooling, and ventilation never get the attention they deserve, most people don't think about what's above the dropped ceiling and just complain about where the thermostat is set. But post-pandemic, employees, their bosses and their landlords are paying a lot more attention. Air quality is suddenly top of mind, and the TRCA building is a wonderful demonstration of where every building should be going.