Wednesday 27 June 2018


Went down to the Wexford Science Café [whc multiprev] last Tuesday because The Lead was going to talk about nZEBs - that would be near Zero Energy Buildings, in which field he has years of expertise. The problem with houses is that they are filled with people, dogs and cats: who breathe (and cook and have baths).  The domestic fridge in the kitchen, if reasonably modern, will run at 150W and cost about 50c/day to keep the contents at an ambient 4oC. Keeping the milk and butter cool will deliver a few Watts of pure heat energy out from the cooling unit to help warm the kitchen. The adults in the house will also be generating about 100W of heat but will also be delivering a bunch of water vapour and carbon-dioxide. The water-vapour from breathing, but also from cooking and washing with large quantities of hot [vaporizing] water has to get out of the building of your kitchen and bathroom walls will quickly become furry. You don't want that, but central-heated houses (of trad or nZEB design) which are dry enough to prevent mold growth are also dry enough to make your lung epithelium dry out. This makes us moderns more prone to sniffles and colds. My Dad used to hang humidifiers on the radiators to wick water from a reservoir and vaporise into the air.

What the nZEB does is reduce the amount of temperature fluctuation through the day. A typical house will have a daily range of temperature of about 10oC from 13oC - 23oC, especially if everyone is absent during the working day. Like the tree falling in the forest which nobody hears, there is no point in keeping the kitchen at 18oC at lunchtime if there is nobody there. Our house, is a very very very nice house, but its capacity for retaining heat is appalling. Get the living-room all toasty with the wood-burning stove and it's gone in a blink if you open the door into the icy hallway beyond. The nZEB home is air-tight and super-well insulated. Once you've got it up to temperature it takes only a trickle of energy to keep it up.

There are a couple issues with this. The first is that the whole house operates as a unit around a fancy heat-exchange unit which pushes out warm, damp, used air and sucks in fresh, drier, colder air from outside. This means that you can get fresh-but-not-Baltic air into the home in December. But it also means that all the rooms in the house are the same temperature. Most people don't want that: they can take it at 18oC in the kitchen because they are moving around chopping, stirring and sieving but that would be a tad too cold if the family is sacked out in the living room watching TV. And many people want it slightly cooler in the bed-rooms . . . after they've finished the bouncy-bouncy and are going to sleep. Those diffs are easier to manage in a traditional home.

I have very direct measured experience of what ambient external temperature is optimal for me. When I went, penniless, to graduate school in Boston in January 1979, I lived in the cellar of my gaffer's home. Nobody in that house walked around, à l'Americain, in tee-shirts in mid-Winter because Neil was in one of his careful-with-money phases. The thermostat was set for 60oF which is 15.5oC. I could work away [in those days I worked all the hours that were not sleeping-hours] it if was 60oF, so long as I had a sweater on. But hot air rises and the forced air heating system made it warmer upstairs than the cellar. What I found was that if the real temperature fell to 59oF = 15.0oC then I just couldn't concentrate even if I wore a coat and hat. That's a rather narrow and precise threshold for sustainable study / reading /calculating.

We were shown a graph of daily temperature fluctuations of a traditional = leaky house vs a nZEB = passivhaus. nZEB is really homeothermic, there is no much insulation and thermal inertia that the temperature is only changing a couple of degrees about, say, 20oC ambient internal. The trad house is all over the place.  It gets quite cold [~13oC] at night, the thermostat kicks in 1 hour before breakfast and the air temp claws up 10oC to 23oC so the kids feel almost too hot in their school uniforms. Within an hour of dispersal to work and school, the house is frezzzing again and the cat has retreated to the hot-press.

That reminded me of my Human Physiology course at The Institute, where our core body temperature is kept at 37oC +/- 1oC. Get dry roasted in a sauna: 37oC; plunge naked into a snow-drift: 37oC; get dressed like Johnny Forty-Coats or like Nadia Comenesci and it's still 37oC.  We know that our sensitivity, not only to light intensity, but also to light wave-length has impact on our health, happiness and immune-system. Maybe, I thought, it's not such a good idea to live in an environment where our external temperature was so tightly controlled. Maybe, I thought, some aspect of our many systems of homeostasis is going to miss a beat or malfunction because there is no external pulse.
Summary: I can't afford to retro-fit our old drafty home into a passivhaus but I'm not sure I want to live in an unvarying temperature whatever the $aving$.

No comments:

Post a Comment