OffGridForGood
Catch, make or grow everything you can.
Originally the plan for off-grid living included a change out our conventional Electric HWT with a new Rheem Heat Pump HWT.
The cost of the Rheem (for my location) is about $2,000 USD. The existing elect HWT is not very old, ie is not due for replacement.
With our recently installed third MPP 6048, the off-grid system is now capable of 19.6kW output and I put the existing HWT on a MTS - so I can switch it back to utility come November when the sun disappears if needs be. With the HWT now on the solar set up, I finally see what power it actually draws, data I never had before.
I had assumed the cold well water generated some large electrical loads for the HWT, and that this would be an advantage for a heat-pump HWT like the Rheem, since we would be able to get double-benefit from the cooling for the house, while heating the water. But that big sticker price lead me to buy more cells for a DIY battery instead of the Rheem, at least for now.
Some data:
When not in use -ie overnight - the existing HWT cycles once every 4-6 hours and consumes 374Wh each cycle. If we don't use any hot water all day, ie like when we are out all day, the 24-hour consumption is only 1.8kWh. This surprised me, since our big side by side fridge uses 1.6kWh/24hrs. I was honestly expecting a lot more consumption from the HWT. Running showers and using hot water moves the daily consuption up to 3-4kWh/day but not anywhere near as high as I was expecting.
So this leads to two questions: First, if the consumption is only 3-4kWh per day, then the benefit from a heat-pump HWT seems to be far less, ie how much cooling can you expect if the BTU load is so low? (1kWh =3412 BTU, so 3-4kWh/day is only 10,000 to 14,000BTU of cooling) leading me to consider the HP-HWT as not such a great option for its' price, especially since in my latitude A/C is generally only a June - August requirement.
Second, If the 4kW load of the HWT cycling is too much, then it could be cut by using 120v instead of 240v and it would just run longer, but at far lower power level, ie about 1/4 of the load but for x4 the time. This would just mean the recovery time is longer, and since the teen-agers are all adults with their own homes now, maybe not a big concern.
For about the same cost as the Rheem, I could get a Senville HP, that would more reliably provide cooling (as needed) for those three hot months, and also provide some heating during the shoulder seasons (sping/fall) when there is some sunlight, especially during spring when we have long sunny days while still cold weather.
Am I missing anything in the logic? I feel like I have already talked myself into the Senville over the Rheem, but maybe you guys will point out some things I have not considered.
The cost of the Rheem (for my location) is about $2,000 USD. The existing elect HWT is not very old, ie is not due for replacement.
With our recently installed third MPP 6048, the off-grid system is now capable of 19.6kW output and I put the existing HWT on a MTS - so I can switch it back to utility come November when the sun disappears if needs be. With the HWT now on the solar set up, I finally see what power it actually draws, data I never had before.
I had assumed the cold well water generated some large electrical loads for the HWT, and that this would be an advantage for a heat-pump HWT like the Rheem, since we would be able to get double-benefit from the cooling for the house, while heating the water. But that big sticker price lead me to buy more cells for a DIY battery instead of the Rheem, at least for now.
Some data:
When not in use -ie overnight - the existing HWT cycles once every 4-6 hours and consumes 374Wh each cycle. If we don't use any hot water all day, ie like when we are out all day, the 24-hour consumption is only 1.8kWh. This surprised me, since our big side by side fridge uses 1.6kWh/24hrs. I was honestly expecting a lot more consumption from the HWT. Running showers and using hot water moves the daily consuption up to 3-4kWh/day but not anywhere near as high as I was expecting.
So this leads to two questions: First, if the consumption is only 3-4kWh per day, then the benefit from a heat-pump HWT seems to be far less, ie how much cooling can you expect if the BTU load is so low? (1kWh =3412 BTU, so 3-4kWh/day is only 10,000 to 14,000BTU of cooling) leading me to consider the HP-HWT as not such a great option for its' price, especially since in my latitude A/C is generally only a June - August requirement.
Second, If the 4kW load of the HWT cycling is too much, then it could be cut by using 120v instead of 240v and it would just run longer, but at far lower power level, ie about 1/4 of the load but for x4 the time. This would just mean the recovery time is longer, and since the teen-agers are all adults with their own homes now, maybe not a big concern.
For about the same cost as the Rheem, I could get a Senville HP, that would more reliably provide cooling (as needed) for those three hot months, and also provide some heating during the shoulder seasons (sping/fall) when there is some sunlight, especially during spring when we have long sunny days while still cold weather.
Am I missing anything in the logic? I feel like I have already talked myself into the Senville over the Rheem, but maybe you guys will point out some things I have not considered.
