Hacker News Reader

Comment by torpfactory | Hacker News Reader

The big issue is timing: hot water, fridge use, and home heating would need to be well synchronized to take advantage of this. I.e. you don't necessarily want to make your fridge colder just because you happen to be heating water. The fridge and temperature is set so your lettuce doesn't freeze and your hamburger says solid. Your water heater turns on because you took a shower. You would need to store the thermal energy (a block of ice, perhaps), but this adds complexity and cost.

View on HN

You don't need to be very optimal to save energy. Your hot water heater is a very good buffer of heat as it stores a massive amount of energy and you don't care if its a few degrees warmer or colder than its set point. In some modern homes the hotwater heater runs far above safe delivery temperature to prevent various issues and is mixed down to a safe temperature elsewhere in the plumbing (either at point of use or in the outlet of the water heater) so the water temperature is even less critical.

The biggest impediment to a system like this is political, as appliance manufactures need to be on board with it, when they have 0 incentive to do so, as their expensive refrigerator becomes a cheap insulated box with a light.

>In some modern homes the hotwater heater runs far above safe delivery temperature

Is this a modern feature? It has been this way for as long as I can remember.

Its complicated, as at first you ran as how as you could to maximize the amount of hot water you had, then there was a period where it was seen as more energy efficient and prevented burns running at lower temperatures. "Modern" practice in this case started somewhere around 1970 where you have a termostatic valve (also called a Tempered Water System) to regulate the temperature of the resulting hot water to non-scalding levels.

Not sure if it's a modern feature per se. But if you have a tankless heater, you can set the temperature to be a little bit above the hottest water you require. If you have a heater with a tank, you need to keep it hot enough to prevent bacterial growth, specifically those that cause legionnaire's disease.

I've seen systems with a tank, heat pump and solar panels, where the system automagically drives up the temperature to kill bacteria every once in a while. Supposedly that's more efficient than keeping it hot all the time.

If the link was optional, so they could either share heat movement or discard waste heat, then there’d be plenty of room for an algorithm to sort it out.

Maybe you can pipe all your heat and cold to central locations and have some kind of heat broker. There’s also a lot of heat in your attic.

perhaps maybe in a large tank of a thermally dense fluid.

But if the link is optional (i.e. no storage), it's unlikely the timing works out often enough to justify the increased complexity or cost. (E.g. if the time overlap of water heating AND fridge cooling is 25% (which seems pretty high to me), you'd only get that percentage of the energy savings.

Reply on news.ycombinator.com