Is Toronto trending towards more heat and humidity like many Japanese cities? The City of Toronto projects that in just 25 years, we will see 66 days where temperatures exceed 30 degrees Celsius, up from 20 days experienced now. Like Japan’s “tsuyu” Ontarians can expect more rain. The mean annual daily maximum of rainfall will be 86mm. Today that number is 48mm.
It’s going to get hotter and wetter, which means, or course, it’s going to get more… sticky.
So what does this mean for high performance houses? Although nothing beats the heat better than superbly installed, air tight insulation detailing, even high performance houses are going to need dehumidification – but a lot less of it and ‘code built’ houses!
It’s not the Heat, it’s the Humidity…
Leave it to Canadians to come up with the “humidex” which incorporates the twin thugs of discomfort; searing heat and punishing humidity. While the radiant summer heat (sensible heat) glides through a glass window and beats through poorly insulated wall and roof details, its brutal, relentless brother – humidity (latent heat ) – piggy-backs on outside air and slips into the house through openings in the home’s shell or worse through open windows. Together, these two brutes can deprive you of sleep and make you cranky as July crawls along.
The energy absorbed into the air’s moisture is significant. It affects our body’s primary mode of being able to cool itself by way of evaporation on the skin through sweating. Air is like a towel; when dry it can dry your skin off to relieve you of heat but if the towel is wet it won’t dry you off leaving you a sweaty mess. Controlling and reducing the levels of indoor humidity – or latent heat – are key to maintaining comfort but also controlling the proliferation of mold growth.
As the Japanese will tell you, festering moldy smells in the home and on furnishings as the summer drags on necessitates strategies to deal with the humidity, some even go as far as seasonally packing fabric goods in air tight containers for the rainy season. As Ontario summers grow long in the tooth, we may find ourselves needing to borrow ideas from the Japanese in managing summer humidity.
Long and Steady
The most efficient air conditioners on the market are mini split heat pump systems the best rate over 30 SEER. The best strategy is to run a smaller system for longer periods of time, and of course ensure that the windows are closed. Why a smaller system? Because large systems tend to lurch on and off frequently and only drop the sensible heat without precipitating as much moisture out of the air as it could. This may leave you feeling cool and sticky and mold blooms may still develop and linger. Besides its really important to give your skin’s natural cooling mechanism a fighting chance by significantly reducing the latent heat (air moisture) in the house.
This is where many mini split heat pumps excel. Not only do they have higher SEER ratings than central forced air units, many also modulate their output without sacrificing efficiency. You can’t do that with a central forced air system. Because mini-split heat pumps draw so little power, the net effect of keeping the system on for longer periods of time won’t impact your energy consumption and will leave you feeling more comfortable. It should be noted that moist air is more buoyant than dry air, so it makes sense to install the air returns high up on the wall, if not on the top floor ceiling.