Off Grid house with Dish TV. Power off or leave on?
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The drawback to using ice, if it can be called that, is probably no real energy use reduction except that from longer and fewer fridge compressor cycles, with that relatively small amount of energy savings being largely offset by a fridge temp. closer to C., instead of maybe something like 4 or 5 C.Last edited by J.P.M.; 01-04-2018, 09:31 PM.Comment
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I suggested ice because of the heat of fusion of H2O, liquid to ice and reversibly the other way around being about 80 times that of the energy required to raise the H2O's temp. 1 degree, meaning the volume of ice can be about 80 times less or a bit more after ice/liquid volume adjustment and thus have the same temp. retention as 80 times the same volume of liquid H2O with the added advantage of lower fridge temps., leaving more room for food storage.
The drawback to using ice, if it can be called that, is probably no real energy use reduction except that from longer and fewer fridge compressor cycles, with that relatively small amount of energy savings being largely offset by a fridge temp. closer to C., instead of maybe something like 4 or 5 C.Last edited by Sunking; 01-05-2018, 12:40 AM.MSEE, PEComment
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Ice in the freezer is a good idea. Ice in the fridge will help with energy, but then you have the make that ice and put it in the fridge every day.Comment
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As for fridge/freezers and discussions discussions here about the rate of change of temp. difference between the inside of a cold(er) space and its surroundings, it makes no difference if the space is a fridge or a (colder) freezer or, say, a warmer oven for that matter. A simple and therefore incomplete but still useful model that uses a lumped mass system and the idea of a thermal time constant can be informative. Without a lot of math, the lumped thermal mass system is analogous to an RC electrical circuit where the thermal capacity ( the lumped mass) is analogous to a circuit capacitor, and the inverse of the rate of overall heat loss in the thermal model is analogous to the circuit resistance.
The gross thermal mass (sometimes called thermal capacitance) divided by the overall heat loss rate per degree of temp. diff. between (the lumped mass system = the fridge and it's contents) and its surroundings is called the thermal time constant of the lumped mass system and has the dimension of time.
So, the larger the thermal mass of a system OR, the lower the heat loss rate (or both) the greater (longer) will be the fridge time constant, and the slower the lumped mass temp. change will be, meaning in our fridge example here, the box will stay cooler longer when it has more stuff in it (or ice as discussed below).
More thermal mass will allow the fridge to cycle less, with each cycle being longer, meaning longer run times but also longer off times - with the longer off times seeming to be the goal here.
FWIW, the same longer cycle times can theoretically and actually be obtained by insulating the crap out of the box which will not only increase the time constant by reducing the overall heat loss rate,. but also reduce the electrical use as well. That ploy however, is fraught with lots of potential and practical problems and I'd not recommend it to the point of saying don't do it.
As for ice in the fridge vs. other things (like beer for example) that don't change phase, ice in the fridge has the advantage of a large latent heat of fusion. So, a kg of ice @ 0 C. will absorb the same amount of heat as 80 times as much liquid H2O at 0 C. and remain at 0 C. until all the ice turns into liquid. That has obvious space saving opportunities. There are some disadvantages of ice in terms of perhaps too cold temps. in a fridge, but a little experimentation with ice quantity and location in the box usually solves that problem. I used plastic gal. jugs filled about 90 -95 % with loose tops. Worked great. Long, boring story.
SK: not a knock, and if you're meaning some (self deprecating ?) humor, please accept my apologies for my slow uptake on the joke, but the proper term (since the mid 19th century anyway) for the branch of science that deals with the relation(s) between heat and other forms of energy, including work, is "thermodynamics" (with, and in light of recent discussions, it ought to be noted, is sometimes first letter capitalized by some). Referring to it as "Thermal Dynamics" is, as you seem to imply, ignorant. Your meaning probably remains clear to most, but, and I'm guessing you care not a whit here, its use doesn't do much to help folks knowledgeable in that area take you as seriously. Analogously to your actions around here, I try to keep my mouth mostly shut about stuff I'm ignorant about, but I know its not called "Elect Ronics".
Respectfully,Last edited by J.P.M.; 01-05-2018, 03:30 PM.Comment
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SK: not a knock, and if you're meaning some (self deprecating ?) humor, please accept my apologies for my slow uptake on the joke, but the proper term (since the mid 19th century anyway) for the branch of science that deals with the relation(s) between heat and other forms of energy, including work, is "thermodynamics" (with, and in light of recent discussions, it ought to be noted, is sometimes first letter capitalized by some). Referring to it as "Thermal Dynamics" is, as you seem to imply, ignorant. Your meaning probably remains clear to most, but, and I'm guessing you care not a whit here, its use doesn't do much to help folks knowledgeable in that area take you as seriously. Analogously to your actions around here, I try to keep my mouth mostly shut about stuff I'm ignorant about, but I know its not called "Elect Ronics".MSEE, PEComment
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No apology needed, it was a joke as indicated by the font I think you caught. Just like my biz, I hired ME's to do HVAC and building mechanical systems. I don't tell them what to do, they just tell me what they need for power requirements. I actually understood most of what you said with relationship to time constants and capacitance. Just not something I do everyday. I can size a heat pump for a house, but I always had someone double check my work. I would never Stamp drawings unless the other disciplines signed off. That is why they get paid the big bucks.
Info was more for others like Cult, with respect to the 2d para. of his 1104 hers. post.
FWIW, the same thermal time constant concept is applicable to time shifting of A/C loads to game a T.O.U. billing system. Sort of like a thermal battery. Or, as a minor advantage,. to increase HVAC cycle times and in so doing reduce startup transient losses and system wear a bit.
Off topic, but the sunspace I added to the first house I owned in Buffalo had about 7,000 lbm of dyed black water contained in translucent 24" dia. 6' long vertical tubes that, along with rather effective and operable thermal shutters, would keep the temp. of the attached space about 30-40 deg. F. above the outside ambient temp. at night with no addition of aux. heat. The water also helped prevent daytime overheating for the ~ 50 - 60hrs./winter month when the solar disk appeared.Comment
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Off topic, but the sunspace I added to the first house I owned in Buffalo had about 7,000 lbm of dyed black water contained in translucent 24" dia. 6' long vertical tubes that, along with rather effective and operable thermal shutters, would keep the temp. of the attached space about 30-40 deg. F. above the outside ambient temp. at night with no addition of aux. heat. The water also helped prevent daytime overheating for the ~ 50 - 60hrs./winter month when the solar disk appeared.
MSEE, PEComment
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The thing stopping you from a lot of that stuff here is the gov't. They don't want anyone living "self-sustaining". They want to steal from all of us here. They fine people here for capturing rain water and now they have these stupid laws or some crap making it so your entire house in Miami cannot be off the grid. They force everyone to be connected to FPL.Comment
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