Tankless water heater

[opendoor]

Originally Posted by Azure

I would be very curious to see some numbers on this.

Alberta doesn't have cold temperatures all winter (chinooks, etc), and you probably have 8 months out of the year where the temperature would be around 10 C? In that situation you aren't actually using a lot of energy to heat your home, and taking the ambient air from your utility room to heat your water shouldn't actually really be removing THAT much heat from the air.

I get that the warmer the climate, the more efficient the get, but I wonder what the line is.

Also, if you have this thing in the basement, and you have floor heat, the radiant heat coming out of the slab in your utility room should really help, and I would think the utility room doesn't have to really be that warm, so its not like you need to recover the heat it pulls out.

Really curious how well it would work.

I mean, there isn't a whole lot to it. If you're pulling 100K btus out of your ambient air to heat your water, you're going to need to replace that during the heating months if it's in a conditioned space. Whether that's forced air, radiant heat, or whatever, or at -30º vs 10º outside, a heat pump water heater is going to drop the air temperature of the room its in and increase the space heating needs by the amount of btus it pulls out of the air. If it's warm enough out that youi're not heating, then it's extremely efficient. But for most of the year, there aren't really any efficiency gains (and it's a net loss in places with electricity that's generated from gas because of the inefficiencies in that process).

In a region with cleaner electricity generation, the environmental benefits vs. gas are worth it. But burning gas to produce electricity and then using that electricity to heat water is way less efficient than just burning gas to heat water, even if you're gaining some efficiency with a heat pump water heater.

[timun]

Alberta has temperatures cold enough to require heating almost all year. One way of expressing the amount of heating required is using heating degree days (HDD), which is calculated as the difference between an idealized indoor temperature of 18 °C and the mean outdoor temperature on a given day (the arithmetic mean between daily max temperature and min temperature, i.e. yesterday the high was 13.2 and the low was 0.8, so the mean between the two was 7.0 °C which means yesterday incurred 18-7 = 11 heating degree days).

Cooling degree days (CDD) are defined the same way, the difference between the mean daily temp and the 18 °C ideal. The annual average CDD over the last 25 years is 58, and last year was waaaaay above average hitting a high water mark of 174. (I looked this up weeks ago for a report I did for a local client that had a big problem with their facility's cooling system last year, haha.) That was almost four standard deviations higher than average; last summer was super unusually hot.

Do you know how many heating degree days Calgary has annually? Remember, by comparison 174 CDD last year was massively higher than usual.








About 5,000.

We need heating waaaaaay more than we need cooling. Mechanical cooling is counterproductive for the vast, vast, vast majority of the time, and that's in effect precisely what a heat pump water heater is: mechanical cooling of our houses.

[Azure]

Originally Posted by opendoor

I mean, there isn't a whole lot to it. If you're pulling 100K btus out of your ambient air to heat your water, you're going to need to replace that during the heating months if it's in a conditioned space. Whether that's forced air, radiant heat, or whatever, or at -30º vs 10º outside, a heat pump water heater is going to drop the air temperature of the room its in and increase the space heating needs by the amount of btus it pulls out of the air. If it's warm enough out that youi're not heating, then it's extremely efficient. But for most of the year, there aren't really any efficiency gains (and it's a net loss in places with electricity that's generated from gas because of the inefficiencies in that process).

In a region with cleaner electricity generation, the environmental benefits vs. gas are worth it. But burning gas to produce electricity and then using that electricity to heat water is way less efficient than just burning gas to heat water, even if you're gaining some efficiency with a heat pump water heater.

Interesting.

So it seems to be more efficient if you have a REALLY warm climate (middle to southern US), or even perhaps if you need a lot of air conditioning in the summer as it can help with that?

Here in Manitoba we have all electric heating, and use heat pumps for air conditioning in the summer (outside air). Works great. Always wondered if it would help to use a heat pump water heater, as it SHOULD be more efficient than a normal Marathon electric hot water tank. And then in the summer you can route the cool air generated from the heat pump hot water heater into your ducting that is used for cooling to help with that.

[opendoor]

Originally Posted by Azure

Interesting.

So it seems to be more efficient if you have a REALLY warm climate (middle to southern US), or even perhaps if you need a lot of air conditioning in the summer as it can help with that?

Here in Manitoba we have all electric heating, and use heat pumps for air conditioning in the summer (outside air). Works great. Always wondered if it would help to use a heat pump water heater, as it SHOULD be more efficient than a normal Marathon electric hot water tank. And then in the summer you can route the cool air generated from the heat pump hot water heater into your ducting that is used for cooling to help with that.

It depends what you're comparing it against. A heat pump water heater will always be more efficient than an electric water heater. So even in a cold climate, a HPWH will save energy vs. a resistance electric water heater simply due to the savings in non-heating months. So even in colder climates, they can be a great idea where electricity is relatively cheap and produced cleanly (i.e. Quebec, Manitoba, BC, etc.) or if you have solar panels.

Where it's not necessarily advantageous is when you're comparing to heating water with gas, and even more so in places where electricity is generated by burning gas. Gas-fired plants are pretty inefficient (~50% I believe) and then you have transmission losses in the electric grid, so it might take twice as much gas to produce a given number of BTUs with electric water heating compared to just heating with gas. So even with the efficiencies gained by a HPWH in non-heating months, there isn't necessarily a benefit environmentally and it's likely significantly more expensive based on the rates timun posted above where per kW (or GJ), electricity is about 5x more expensive than gas in Alberta.


So basically, if the electricity generation is largely non-fossil fuel and relatively inexpensive, then HPWHs definitely make sense. And the warmer the climate (fewer heating days) the more efficient they are.