System 6.7 kWh + 2 PowerWalls - Will It Cover 100% of my Usage?

[sorka]

I have so much excess generation, I can do whatever. Now we shall see if thats too cold for her, if so we will try 76. And since I run off batteries 100% after 30, and basically all solar before, I prepaid for all this furn My wife wants it cold. So next winter, rather than my 60 degree, want to do 66 or 68. For 30 years never could do any of this, house to big and expensive. But with solar (any maybe more), and batteries, I can do ANYTHING!!!!

 

[sorka]

Both my ACs are the original units from 1998. They are SEER 11. If at the end of the summer we ended up using way more than expected, then I'll replace them with SEER 26 units. They're due to be replaced anyways. They've never been serviced. I've checked the condenser fins every 5 years but they're always perfectly clean.

 

[getakey]

Both my ACs are the original units from 1998. They are SEER 11. If at the end of the summer we ended up using way more than expected, then I'll replace them with SEER 26 units. They're due to be replaced anyways. They've never been serviced. I've checked the condenser fins every 5 years but they're always perfectly clean.

If you have excess solar, think about a heat pump as a replacement. Thats what we did with one of our units

 

[holeydonut]

We're about to hit air conditioning season next month. We're going to probably use twice as much AC as we used because "we have solar"

Lol my family didn't curtail any AC before solar; I don't expect any change after solar in this household.

I'm just hoping these Powerwalls get us from 3pm to midnight...

 

[sorka]

If you have excess solar, think about a heat pump as a replacement. Thats what we did with one of our units

Is there a difference between a heat pump HVAC unit for AC cooling? Big difference for heating obviously as they extract heat from outside and move it inside vs burning fuel to create heat but that's exactly how an AC works but in reverse.

We are looking at a heat pump hybrid water heater for our next water heater. The fit is better because when it's really hot outside, we want to transfer that heat to water even when we're cooling inside which makes the hybrid water heaters incredibly. In fact, it's about half the cost in electricity compared to Propane.

But heating the inside when it's freezing outside is nowhere near as efficient. Heat pump heaters are best suited keeping your home a little bit warmer than it is outside. The problem is our house is warm enough in the winter when it's freezing outside, that we'd have a hard time raising the temperature more than it already is without heating.

 

[holeydonut]

Is there a difference between a heat pump HVAC unit for AC cooling? Big difference for heating obviously as they extract heat from outside and move it inside vs burning fuel to create heat but that's exactly how an AC works but in reverse.

We are looking at a heat pump hybrid water heater for our next water heater. The fit is better because when it's really hot outside, we want to transfer that heat to water even when we're cooling inside which makes the hybrid water heaters incredibly. In fact, it's about half the cost in electricity compared to Propane.

But heating the inside when it's freezing outside is nowhere near as efficient. Heat pump heaters are best suited keeping your home a little bit warmer than it is outside. The problem is our house is warm enough in the winter when it's freezing outside, that we'd have a hard time raising the temperature more than it already is without heating.

A heat pump still has a compressor and evaporator coil. So I think for general purposes, a heat pump behaves the same on the cooling cycle as a dedicated condensing unit outdoors. I don't think a regular occupant in a home with a heat pump will be able to tell the difference with a standard outdoor condenser on the cooling cycle.

I think for California's climate, it doesn't get so cold that the heat pump will stop being effective for heating. But the term "effective" takes on different meaning depending on who you speak with.

I think where people have issues with the "effectiveness" of a heat pump isn't whether it can get a house up to 70F. The issue is usually the lag time between the heat pump turning on, and nice warm air hitting their face. Like if someone gets out of the shower when a normal gas furnace is running, then nice warm air hits them. But if the same person gets out of the shower with a heat pump, then lukewarm air hits them.

So while I like heat pumps for their operational ability to pull heat into a home, I do not trust them to deliver the instant-on type of thing that burning some dead dinosaur farts can produce. I believe a household will see a rise of complaints if they go from a gas-furnace + air handler and switch to a heat pump. I think even if you got radiant heating flooring plus a heat pump there would still be gripes.

But if that household were to want to help save the planet, being a bit colder stepping out of the shower may be an ok trade-off? Bah, what am I saying. This is 'murica... let's burn some clean coal and clean natural gas...

 

[sorka]

A heat pump still has a compressor and evaporator coil. So I think for general purposes, a heat pump behaves the same on the cooling cycle as a dedicated condensing unit outdoors. I don't think a regular occupant in a home with a heat pump will be able to tell the difference with a standard outdoor condenser on the cooling cycle.

I think for California's climate, it doesn't get so cold that the heat pump will stop being effective for heating. But the term "effective" takes on different meaning depending on who you speak with.

Maybe if you live near the coast. I live inland where it's in the 30s every night and 40s or 50s during the day in the winter.

 

[holeydonut]

Maybe if you live near the coast. I live inland where it's in the 30s every night and 40s or 50s during the day in the winter.

IMO, 20F should be easy peasy for a new scroll compressor heat pump.

Heat Pumps: A Practical Solution for Cold Climates - RMI

It’s almost winter in the Northern Hemisphere; time for people to snuggle up with their families (including the four-legged members), cultivate the now-international practice of hygge, and find other ways to deal with the relative lack of sun. The cold is coming, and with it comes the question...

rmi.org

Anyway I wouldn’t get a heat pump simply because burning dinosaur farts heats way better and I couldn’t get enough solar to power these things.

 

[getakey]

I got a heat pump with NG backup. You can set the temp at which the heat pump uses gas instead of electricity. If you already have gas, its a good option

 

[BGbreeder]

I think that there is also a change in thermostat and fan usage moving from gas/propane to heat pumps.

Gas/propane furnaces come on and produce large amounts of hot air quickly. Turning down the temp at night can save energy,

Heat pumps produce warm air, and tend to have significantly lower BTU ratings, so they tend to run longer/more frequently. The constant air flow keeps air from stratifying in rooms as much, but it takes much longer to warm / cool a house. As a result, heat pumps tend to be set at one temperature for 24x7, and by design run a large fraction of the day. As the fans tend to be variable speed, heat pumps tend to be quieter than fueled furnaces.

For those thinking about resilience, getting through a few weeks in winter with a normal size solar PV, powerwalls, and a heat pump would be cold without some backup heat source. In contras, solar, powerwalls and propane, weeks are possible.

Older heat pumps suffered with poor performance below freezing, but the new designs and refrigerants enable heating well below 0F. One brand advertises -40F, without heaters.

Heat pump water heaters have, to me, incredibly low power draw, but they are louder than a gas/propane furnace. Much louder, 50-60db, so if your hot water heater is adjacent to living and especially sleeping spaces, HPWH may not be a good fit unless they get relocated. Due to minor things like backup cooling coils/less insulation, they tend to lose more heat compared to other designs.

All the best,

BG

 

[tomuo]

Is there a difference between a heat pump HVAC unit for AC cooling? Big difference for heating obviously as they extract heat from outside and move it inside vs burning fuel to create heat but that's exactly how an AC works but in reverse.

We are looking at a heat pump hybrid water heater for our next water heater. The fit is better because when it's really hot outside, we want to transfer that heat to water even when we're cooling inside which makes the hybrid water heaters incredibly. In fact, it's about half the cost in electricity compared to Propane.

But heating the inside when it's freezing outside is nowhere near as efficient. Heat pump heaters are best suited keeping your home a little bit warmer than it is outside. The problem is our house is warm enough in the winter when it's freezing outside, that we'd have a hard time raising the temperature more than it already is without heating.

I switched to Heat Pump cooling / heating.
In Los Angeles, our AC unit was about 35 years old and oversized due to the house being poorly insulated.
The air warmth is less than when it was being fired by gas, but it's still over 90F when the air temp outside was in the 40s, so plenty warm enough to get the house to a comfortable temp. I really don't notice that it takes longer than gas would have at 110F air temp, which needs some extra fan time & mixing to avoid hot spots.
In terms of cooling capacity, there's no difference.

Now one question I have is, when any unit advertises SEER > 20, they can only reach that because they are 2 speed / stage, and can use less energy when the target temp is not far away from current temp. That implies that you need to keep them running longer so there is less time spent at large temps differences.
In my climate, I prefer to keep just the fan running and live in a wider comfort zone rather than have it consuming power to keep it at the exact same temp all day, so a single stage is plenty.

 

[sorka]

I switched to Heat Pump cooling / heating.
In Los Angeles, our AC unit was about 35 years old and oversized due to the house being poorly insulated.
The air warmth is less than when it was being fired by gas, but it's still over 90F when the air temp outside was in the 40s, so plenty warm enough to get the house to a comfortable temp. I really don't notice that it takes longer than gas would have at 110F air temp, which needs some extra fan time & mixing to avoid hot spots.
In terms of cooling capacity, there's no difference.

Now one question I have is, when any unit advertises SEER > 20, they can only reach that because they are 2 speed / stage, and can use less energy when the target temp is not far away from current temp. That implies that you need to keep them running longer so there is less time spent at large temps differences.
In my climate, I prefer to keep just the fan running and live in a wider comfort zone rather than have it consuming power to keep it at the exact same temp all day, so a single stage is plenty.

My next HVAC units will definitely be variable load. Once the set point is hit, I don't want to hear them and the temp will be completely 100% stable.

 

[dareed1]

We have a Mitsubishi heat pump with 30,000 BTUh capability which services a heating load of 26,000 BTUh for a 40F interior-exterior temperature difference (Manual J calculation). The temperature fluctuates up to 2F about the setpoint--I suspect that the thermostat system temperature resolution is 0.9F (0.5C), which is too coarse for fine temperature control. The fluctuation are very gradual, taking hours to drift 1F. However, the 3 speed fan operates on the lowest speed all the time (even if the compressor isn't running--that's configurable), and the air noise is imperceptible except within a few feet of the single air return duct. So the house feels like the temperature doesn't change. Fan power consumption is 50 watts.

Of course, we don't drop the temperature at night because the system doesn't have much spare capacity to quickly increase the temperature of the house. Yes, during cold exterior temperatures, the compressor operates 100% of the time, but at varying power consumption as the heat load changes. My wife very much likes the way this operates compared to our previous oversized gas furnace which had a lot of air noise when it was running, with large temperature fluctuations.

I sized the system this way because I believe it maximizes the efficiency, not so much for financial reasons but instead to maximize the duration the PWs can operate during a grid outage.

 

[h2ofun]

We have a Mitsubishi heat pump with 30,000 BTUh capability which services a heating load of 26,000 BTUh for a 40F interior-exterior temperature difference (Manual J calculation). The temperature fluctuates up to 2F about the setpoint--I suspect that the thermostat system temperature resolution is 0.9F (0.5C), which is too coarse for fine temperature control. The fluctuation are very gradual, taking hours to drift 1F. However, the 3 speed fan operates on the lowest speed all the time (even if the compressor isn't running--that's configurable), and the air noise is imperceptible except within a few feet of the single air return duct. So the house feels like the temperature doesn't change. Fan power consumption is 50 watts.

Of course, we don't drop the temperature at night because the system doesn't have much spare capacity to quickly increase the temperature of the house. Yes, during cold exterior temperatures, the compressor operates 100% of the time, but at varying power consumption as the heat load changes. My wife very much likes the way this operates compared to our previous oversized gas furnace which had a lot of air noise when it was running, with large temperature fluctuations.

I sized the system this way because I believe it maximizes the efficiency, not so much for financial reasons but instead to maximize the duration the PWs can operate during a grid outage.

I have mits mini splits. I have been able to shut it down at night. Meaning, I get up in the morning, turn on my whole house fan, when its in the 50''s outside, and cool the house down 10 degrees. Then, at the moment meaning the killer heat has not started yet, I turn them to 74 at 3pmish when the house hits 73. I then turn them off after dinner. Repeat. Now, when its supposed to be 100 monday, and low 70, will have to do different things. So, I just adjust to run them only when needed. But as you say, trick is to NOT try and get a huge temp drop or rise.

 

[sorka]

I have mits mini splits. I have been able to shut it down at night. Meaning, I get up in the morning, turn on my whole house fan, when its in the 50''s outside, and cool the house down 10 degrees. Then, at the moment meaning the killer heat has not started yet, I turn them to 74 at 3pmish when the house hits 73. I then turn them off after dinner. Repeat. Now, when its supposed to be 100 monday, and low 70, will have to do different things. So, I just adjust to run them only when needed. But as you say, trick is to NOT try and get a huge temp drop or rise.

But if you have a whole house fan you want to get the largest drop that you can. We have a 48" Triangle belt drive fan that is quieter than our HVAC but moves huge amounts of air. The only time we can't use it is during that few weeks in the summer where it doesn't drop below 80F even at 5 am.

 

[h2ofun]

But if you have a whole house fan you want to get the largest drop that you can. We have a 48" Triangle belt drive fan that is quieter than our HVAC but moves huge amounts of air. The only time we can't use it is during that few weeks in the summer where it doesn't drop below 80F even at 5 am.

Mine is SUPER noisy I need something new and quiet. What do you have?

 

[sorka]

Mine is SUPER noisy I need something new and quiet. What do you have?

Triangle 2 Speed 48 inch Whole House Fan 4000 Sq. Ft. Max Belt Drive CC4823

The one I had before was a 30" direct drive unit that was loud and buzzy. The only noise this Triangle fan makes is the noise of air movement. You can't hear the motor.

The other trick is to build a box to keep it directly off the ceiling:

 

[holeydonut]

I think there was a post a while back about Quietcool whole house fans. I'm not schilling that vendor, but they use variable speed ECM motors instead of what appears to be a PSC style motor on the Triangle whole house fan. I think you should check out ECM for the flexibility to run at lower speeds. For disclosure, I don't have a whole house fan, and I don't like them because of my allergies.

Based on the spec sheet of Triangle's PMTR-CC3623 (motor used in the fan that sorka linked), says it is 8.2A at 115v on high ... so it's around 950w. The low setting isn't described, but since PSC motors aren't linear, I'd expect low to pull over 600w.

The largest Quietcool ES7000 ranges from 276w up to 1,100w. But I really don't think you get much bang for your buck with these attic fans on their high setting. So it's likely you'll just use this thing on medium for a few hours around sunrise and sunset to move some cooler air from outside inside to get some cooling that is more efficient than an AC.

My 2 stage Lennox + internal air handler takes 1.7 kW. IMO, I'd rather just run my ACs if the trade off is a 1kW whole house fan running on high trying to blow air around.

 

[h2ofun]

Triangle 2 Speed 48 inch Whole House Fan 4000 Sq. Ft. Max Belt Drive CC4823

The one I had before was a 30" direct drive unit that was loud and buzzy. The only noise this Triangle fan makes is the noise of air movement. You can't hear the motor.

The other trick is to build a box to keep it directly off the ceiling:

Interesting, I have a 30 inch. We cut the joist to put in. It is very loud!! So, I could not find any DB specs for these. But since seems the same as what I have now, is how is the triangle fans quieter when it looks the same?

 

[holeydonut]

Interesting, I have a 30 inch. We cut the joist to put in. It is very loud!! So, I could not find any DB specs for these. But since seems the same as what I have now, is how is the triangle fans quieter when it looks the same?

I think he kind of answered your question already... he built a box that elevates the fan away from the joists and adds some more reinforcement. Maybe he even put some EPDM or bushing stuff under his box to further create some dampening between the big azzz fan and the ceiling.