Solar with Heat Pump for Heating/Cooling House

[abasile]

I'm hoping to install an air-sourced heat pump eventually, so I appreciate this thread.

On a similar topic, can anyone recommend a family-sized heat pump clothes dryer? Both LG and Whirlpool sell these, but the reviews aren't great and the reliability seems questionable. Besides using a clothesline, how are folks with net-zero homes drying their clothes?

Due to our home being three stories tall with significant shading, we don't have enough roof space to offset all of our electric usage with PV (mostly because our EVs get driven a lot). We have natural gas service, but I'd rather not have to buy another appliance that burns fossil fuels. At the same time, running a standard electric dryer on grid electricity (even in California) is more carbon intensive than running a gas dryer. So we might be stuck with gas for a while.

I've been through the same thought process with water heaters, but it appears that it's currently quite expensive (> $3k) to acquire a heat pump water heater that would be suitable for use in a cabinet on the exterior of a home in a cool climate with freezing winter temperatures. Thankfully, our gas water heater is working fine right now, so I can wait for the tech and prices to improve.

 

[Ampster]

.....how are folks with net-zero homes drying their clothes?

I am not there yet, as far as ner zero, but when I bought the home I put in an electric dryer. The laundry room has both gas and electric hookups. I also looked at heat pump clothes dryers and concluded they weren't ready fo prime time. I purchased a high end Samsung and it does have an Eco mode. All that means is the heat doesnt cycle as often and cloths take twice as long to dry.

 

[Zythryn]

Besides using a clothesline, how are folks with net-zero homes drying their clothes?

We dry most of our clothes on drying racks.
We did get the Whirlpool ventless dryer based on heat pump technology.
We have had it just under 2 years, no issues with it so far, we are quite happy with its performance.

This was one of the big wastes of energy in the winter, so we went for it. The costs are high though, and I am sure the companies are still learning about the technology.

 

[Jigglypuff]

If your washer spins fast enough, the dryer won't need to work so hard.

 

[abasile]

If your washer spins fast enough, the dryer won't need to work so hard.

Very good point. We're going to be looking for a washer that does a really good job spinning out the rinse water.

We did get the Whirlpool ventless dryer based on heat pump technology.
We have had it just under 2 years, no issues with it so far, we are quite happy with its performance.

It's great to know that this dryer has worked well for you. However, there are just too many negative reviews for me to feel comfortable plopping down $1500 or so for it. I hope that your dryer continues to serve you well. Perhaps it helps that you're not using it all of the time.

Again, it seems that for non-heat-pump electric dryers, the "long tailpipe" argument unfortunately has merit, even on today's California grid. I'd love to be proven wrong. We still have quite a ways to go to de-carbonize our everyday appliance usage!

 

[Zythryn]

The CA grid is dirtier than 100% natural gas?
I’m quite surprised at that, or am I misunderstanding?

The huge energy loss of dryers is the fact that you are taking a lot of conditioned air from inside the house and expelling it outside.

Read those reviews carefully, as many maybe due to the humidity and/or heat in the laundry room the results from running the dryer.
I can see how, if you weren’t aware of it, would be disturbing.
For us, this isn’t an issue. In the winter it is quite welcome. In the summer we leave the doors closed in the laundry room and let the hvac take care of the issue. It is much less of a moisture issue than a shower steaming up a bathroom.

In any event, a drying rack or clothesline is the most energy efficient

 

[wwhitney]

The CA grid is dirtier than 100% natural gas?
I’m quite surprised at that, or am I misunderstanding?

When it comes to heating water, it may be:

If you are comparing the carbon usage of gas tank water heaters to electric resistance tank water heaters, then you need to know the carbon content of the grid electricity. Modern natural gas generators are apparently in the 50% to 60% efficient range, call it 55%. The energy factor of a standard electric resistance tank water heater is typically 0.9, so the total thermal efficiency is about 50%. While the energy factor of a standard natural gas tank water heater is typically 0.6, so the total thermal efficiency is about 60%.

Thus if the grid were 100% modern natural gas generators, you'd be using more carbon to heat your water with an electric resistance tank water heater than a gas tank water, by a factor of 6/5. The grid obviously has some more carbon intensive generators and some less carbon intensive generators. So the actual answer will depend on the grid makeup.

Cheers, Wayne

 

[abasile]

Read those reviews carefully, as many maybe due to the humidity and/or heat in the laundry room the results from running the dryer.

It's true that some of the negative reviews of heat pump dryers were due to the moisture and heat introduced into living space. While this wouldn't be bad during winter, and wouldn't be a showstopper for us, it's a negative for us overall (we don't have A/C at this point). However, I'm more concerned by a number of reviews which seem to point to longterm reliability issues arising from lint gumming up the relatively closed system.

In general, there seems to be surprisingly little available information to help climate-conscious consumers decide between dryer technologies. Here's one of the better sources I found, from NRDC, albeit a little dated (2011): https://www.nrdc.org/sites/default/files/ene_14060901a.pdf

That NRDC report, and various other sources, indicate that the on-site energy consumption of a standard electric dryer is only slightly less than that of a comparable gas dryer. For "high-end" electric and gas dryers, the cited DOE figures are 747 kWh-e / year and 758 kWh-e / year, respectively for normal usage.

To roughly compare climate impact in California, here are my calculations:

For the gas dryer, suppose 3% of natural gas is lost in transmission and distribution. For the gas dryer, per year, you need 758 kWh-e / 0.97 = 781 kWh-e of source fossil fuels. Note that this figure ignores the greater short-term impact of methane leakage (relative to CO2 emissions), and it also ignores the fact that some of the input energy is coming from the electric grid (to run the motor and electronics). To roughly account for this, let's round up to 800 kWh-e "carbon equivalent".

For the electric dryer, I'll choose some slightly optimistic numbers; after all, the California grid is getter cleaner each year, and a new dryer should last 10-15 years. Suppose 40% of grid power is from near-zero carbon sources including renewables, hydropower, and nuclear. Suppose the remaining 60% of grid power is generated from fossil fuels at an average efficiency of 50%. Suppose that transmission losses are 5%. Per year, of the 747 kWh required, you get 40% "for free" from a CO2 emissions standpoint, leaving 448 kWh / 95% (after transmission) = 472 kWh that needs to be generated from fossil fuels. At 50% efficiency, that translates to 944 kWh-e of source fossil fuels or "carbon equivalent".

So, it appears that running a high-end gas dryer might have about 80% or 90% of the climate impact of a high-end electric dryer on the California grid. If even a fraction of the electric dryer's consumption can be offset by home solar PV, then it seems like a clear winner. Also, electric dryers are easier to install, probably safer, cheaper, and average slightly shorter drying times. On the other hand, natural gas is probably a good deal cheaper than grid electricity.

 

[Jigglypuff]

Solar investment covers my electric inefficiencies. I mainly don't want to pay the insane propane prices around here. If I could get natural gas here, I'd run it in my water heater and furnace, no hesitation. However, I'd want some kind of electric heat backup for when disaster strikes.