ajdelange
Well-known member
- First Name
- A. J.
- Joined
- Dec 8, 2019
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- Virginia/Quebec
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- Tesla X LR+, Lexus SUV, Toyota SR5, Toyota Landcruiser
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- EE (Retired)
I thought we were talking about whether the CT would handle a whole house in an emergency. I am saying that based on the fact that I weathered many a power outage on a 7 kW generator for years and that I expect, therefore, that I would be able to do it with the 7 kW inverter in the CT (as long as the battery lasts anyway). It is so obvious that some sort of load management is/would be
required that I didn't feel it necessary to discuss it explicitly until it appeared this was an unfamiliar concept to you and so I didn't until No. 29.
So let's go a bit more into how you would manage loads manually if running my whole house on a 7 kW inverter. In particular let's talk a bit about how I would have done that on the most demanding day of last winter which was February 7th on which day average consumption was 5.71 kW with a crest factor of 2.5 (peak demand 14 kW). Load was less than 7 kW 61.4% of the time but it was over the remaining 38.6. Here's the history:
The long pole in the tent is the heat pump. It's probably obvious that its compressors are the cause of the 5 kW "pulses". It's clear that in the middle of the night the baseline load is 1.5 kW and it is also clear that loads other than the heat pump climb to around 4 kW later in the day. To run on the 7 kW generator or inverter we have to keep the total load below 7 kW (unless the duration is very brief).
So we suppose that on that day we awake and it's colder that a well diggers behind because the power went out. What do we do? Haul out of bed, go out to the garage, fire up that generator, go outside and open the disconnect to the panel. Go to the panel, open its feed breaker and all breakers except for some light, comms, the well, some outlets, the refrigerator and the heating systems control transformer. This removes all the loads except the baseline 1.5 kW and you should be able to go 100 hrs on 100 kWh from the battery. But no heat? Not acceptable. What would happen chez mois is that the thermostats would detect that their calls for heat are going unanswered and they would call for E-heat thus firing up the backup propane boiler and the house would come to temperature.
So what happens now. The heat pumps won't run and you have no heat. After a few minutes of no heat the thermostats will call for E-heat. That doesn't do anything for those heatpumps that have electric E-heaters but the one in my house that is backed up with an gas boiler (which also does instant on DHW) fires up and the part of the house you are in warms up (and warms up faster than it does with the heat pump).
Given this I would hope you would be able to see that I could have run my house on that coldest winter day on a 7 kW generator and did so many time largely because the heat pump gets taken out of the equation. In summer time there is no gas backup for the heat pump so the solution is to not run the A/C or run it when all the other loads have been turned off by flipping their breakers. This clearly requires a lot of manual intervention and is a big PITA but it can be done. I've done it. The ability to do it depends in no small measure on the fact that the system is designed to be operated on backup power supplies. That's why the DHW and heating backup are from a gas boiler which operates on only a few watts of electricity.
I will comment that if you have an electric whole house instant on hot water heater you are pretty much out of luck with respect to emergencies. Some of these things draw 36 kW and to run it you need a 36 kW generator. This is not a small generator but many houses do have them in that size and even larger.
required that I didn't feel it necessary to discuss it explicitly until it appeared this was an unfamiliar concept to you and so I didn't until No. 29.
So let's go a bit more into how you would manage loads manually if running my whole house on a 7 kW inverter. In particular let's talk a bit about how I would have done that on the most demanding day of last winter which was February 7th on which day average consumption was 5.71 kW with a crest factor of 2.5 (peak demand 14 kW). Load was less than 7 kW 61.4% of the time but it was over the remaining 38.6. Here's the history:
The long pole in the tent is the heat pump. It's probably obvious that its compressors are the cause of the 5 kW "pulses". It's clear that in the middle of the night the baseline load is 1.5 kW and it is also clear that loads other than the heat pump climb to around 4 kW later in the day. To run on the 7 kW generator or inverter we have to keep the total load below 7 kW (unless the duration is very brief).
So we suppose that on that day we awake and it's colder that a well diggers behind because the power went out. What do we do? Haul out of bed, go out to the garage, fire up that generator, go outside and open the disconnect to the panel. Go to the panel, open its feed breaker and all breakers except for some light, comms, the well, some outlets, the refrigerator and the heating systems control transformer. This removes all the loads except the baseline 1.5 kW and you should be able to go 100 hrs on 100 kWh from the battery. But no heat? Not acceptable. What would happen chez mois is that the thermostats would detect that their calls for heat are going unanswered and they would call for E-heat thus firing up the backup propane boiler and the house would come to temperature.
So what happens now. The heat pumps won't run and you have no heat. After a few minutes of no heat the thermostats will call for E-heat. That doesn't do anything for those heatpumps that have electric E-heaters but the one in my house that is backed up with an gas boiler (which also does instant on DHW) fires up and the part of the house you are in warms up (and warms up faster than it does with the heat pump).
Given this I would hope you would be able to see that I could have run my house on that coldest winter day on a 7 kW generator and did so many time largely because the heat pump gets taken out of the equation. In summer time there is no gas backup for the heat pump so the solution is to not run the A/C or run it when all the other loads have been turned off by flipping their breakers. This clearly requires a lot of manual intervention and is a big PITA but it can be done. I've done it. The ability to do it depends in no small measure on the fact that the system is designed to be operated on backup power supplies. That's why the DHW and heating backup are from a gas boiler which operates on only a few watts of electricity.
I will comment that if you have an electric whole house instant on hot water heater you are pretty much out of luck with respect to emergencies. Some of these things draw 36 kW and to run it you need a 36 kW generator. This is not a small generator but many houses do have them in that size and even larger.
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