Hacker News Reader

Comment by nine_k | Hacker News Reader

I suppose that heat exchanger ventilation makes most sense at winter time. Not everybody lives in San Diego, a lot of people live in New York, Boston, Chicago, Seattle, etc, where a winter is a thing.

View on HN

You can understand quantitatively how this goes for different areas using Heating degree days and Cooling degree days, factoring in latent heat in both cases, ideally. There are calculators for this. I made a spreadsheet on my website www.openerv.ca that shows some of how to reckon this, there are links in there to get data.

In Austin, texas, I think you got quite a bit more energy and money saved per year from avoiding cooling costs, but in Ottawa, Canada, you save about 100x as much in winter as you ever could in summer.

thanks, this is fantastic information!

Also during hot summer when outside temperature is hotter than inside - you don't want ventilation to bring in hot air.

i think heat exchanger ventilation makes roughly the same amount of sense whenever you're spending costly energy to change the temperature of your space, doesn't it? it works just as well to keep summer heat out as to keep winter heat in, and staying cool in summer can be just as critical as staying warm in winter, depending on where you live

the main difference is that you can heat up a house (inefficiently) with a nichrome wire or a gas burner, while cooling it requires considerably more elaborate equipment

but if electricity costs 2¢ per kilowatt hour and daytime electricity is free, will the savings of a heat exchanger be enough to pay for the device?

Electricity here is €0,30-0,40/kWh after tax. (Netherlands) (For fixed contact, dynamic contacts have bigger variation). That makes it way more interesting to save on energy. Although getting solar panels is still the fastest investment. Heat pumps typically have 10-15years payback time, especially now they are insanely overpriced due to Ukrainian-Russian war and climate goals increasing demand and lowering supply.

so when electricity costs drop by 15–20× the payback time will be 150–300 years?

The temperature difference most home heaters work on is much higher than the one most home coolers work on.

Using a regenerator to get 5°C of cooling back with some 30% of efficiency probably won't be cost-effectice. But if you have to heat by some 30°C, the numbers change a lot.

hmm, are you saying that the regenerator (or recuperator) has lower efficiency at lower ΔT? or lower efficiency when it's more a ΔH than a ΔT? because if that 5° of cooling and dehumidification costs you the same US$100 a month as the 30° of heating, saving 80% of it will still be US$80 a month

Winter has much less sunlight, so powering a heat pump via solar panels + moderate battery becomes much harder. It's no longer mostly free.

Reply on news.ycombinator.com