Help sizing freezer Steca PF 240

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izentrop
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Re: Help sizing freezer Steca PF 240




by izentrop » 27/04/16, 12:41

chatelot wrote:a 24V freezer is not the only solution: I prefer an ordinary 220V freezer and an inverter: current inverters have good performance, and 220V freezers are so much cheaper than it pays the inverter
+1
other original solution: use a very well insulated freezer and only run the compressor when the sun is shining: you can do without complete sun: this solution is useful if the freezer is mainly used for storing, if it has to freeze large quantity, you necessarily need batteries allowing the compressor to turn when you introduce the stuff to freeze
Or insulating it can save consumption (50% and more) and shelf life http://forum-photovoltaique.fr/viewtopi ... 99#p369274 ou http://coolfridge.blogspot.fr/
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Re: Help sizing freezer Steca PF 240




by Obamot » 27/04/16, 13:10

izentrop wrote:
chatelot wrote:a 24V freezer is not the only solution: I prefer an ordinary 220V freezer and an inverter: current inverters have good performance, and 220V freezers are so much cheaper than it pays the inverter
+1

This is also what I suggested from the start ^^

izentrop wrote:
chatelot wrote:other original solution: use a very well insulated freezer and only run the compressor when the sun is shining: you can do without complete sun: this solution is useful if the freezer is mainly used for storing, if it has to freeze large quantity, you necessarily need batteries allowing the compressor to turn when you introduce the stuff to freeze
Or insulating it can save consumption (50% and more) and shelf life http://forum-photovoltaique.fr/viewtopi ... 99#p369274 ou http://coolfridge.blogspot.fr/

It is difficult to over-insulate a freezer (if not impossible) if the compressor is part of the body of the equipment, quite simply because the radiator and the compressor produce heat which must be evacuated! In principle, this is only possible in high-end industrial or artisanal refrigeration installations and in any case not on a 24V model. So as already suggested, it is better to take a very good “lambda” one, as isolated as possible (and renamed) from the start with the compressor “going well”. Everything else is bogus savings (and IMHO).

Thanks to Chatelot for clarifying the idea for which it was better to have a "well made" lambda freezer rather than a 24V (expensive and with technical limitations), since this is what I also suggested (but I had forgotten the inverter, since my small generator was equipped with it). On the other hand, we do not yet know all of Kaou's prerogatives.
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Re: Help sizing freezer Steca PF 240




by izentrop » 27/04/16, 13:30

obamot wrote:It is difficult to over-insulate a freezer (see impossible) if the compressor is part of the body of the equipment, simply because the radiator and the compressor produce heat which must be removed!
Obviously, you must insert the additional insulation behind the grid and not in front : Wink: .
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Re: Help sizing freezer Steca PF 240




by kau » 27/04/16, 13:59

Geniuses : Mrgreen:
It was the ideas and the answers that I was looking for, and little by little we came to the solution. Thank you Experts 8) .
The goal is to make 1L sachets of ice cream for sale the same as on the image:
Image

I need on average between 100 and 120 units per day. I know very well that I must not exceed a certain quantity to succeed in getting out of it about fifty a day.
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Re: Help sizing freezer Steca PF 240




by Obamot » 27/04/16, 14:02

Yes, I suspected it was for that!
Because seeing no ad to sell second-hand freezers in Mali, and the ice-cream vendors making their butter along the roads, I thought it could be the goal ^^

There your system will be in constant demand, so no joke, you need a solution "that holds the road" and not improvisation.
It is necessary to take care of a good location of the freezer, the best would be to bury it by making a small cellar in cement and in the shade of the house (which you could cover the day but by letting the heat evacuate from above , while the cold remains below ...)
Then, contrary to what has been said, it is better to produce using the batteries at night (since it is cooler at night the compressor will work less), because the day with 40 ° C it will not be easy! You must therefore oversize the installation accordingly (panels / battery) ... Beware of a crucial point: make sure that the installation is tamper-proof so that the panels are not stolen ...! (This was my main concern ...)

You would have to find square and flexible molds in which you could put your plastic bags so that they match the shape (sort of cardboard or rather plastic? It must be flexible since the ice changes in volume), so that it is possible to put more by freezing ... (well it's optimization, what ...)

But basically, if I were to do this, I would have two types of freezes. A very efficient to freeze and others that would need to be much less to be used only for storage! Besides, in the limit, a shaded cellar with a thick cover and expanded polystyrene walls should be enough, since the ice blocks are used to keep the temperature as low as possible and the cold cannot escape!

izentrop wrote:
obamot wrote:It is difficult to over-insulate a freezer (see impossible) if the compressor is part of the body of the equipment, simply because the radiator and the compressor produce heat which must be removed!
Obviously, you must insert the additional insulation behind the grid and not in front : Wink: .

Except that there is very little space between the two, so with insignificant gain if we add insulation ... Which would also be nonsense, since it would be added over the metal walls which are a good thermal conductor! It would therefore be necessary to isolate the entire body of the freezer in a hermetic manner in order to be able to measure a significant difference in magnitude: eXergie (but this would be to fight against the thermal inertia of the metal walls ... and that does not absolutely not worth it ...)
Last edited by Obamot the 27 / 04 / 16, 14: 25, 1 edited once.
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Re: Help sizing freezer Steca PF 240




by Gaston » 27/04/16, 14:18

kaou wrote:The goal is to make 1L sachets of ice cream for sale the same as on the image:

I need on average between 100 and 120 units per day. I know very well that I must not exceed a certain quantity to succeed in getting out of it about fifty a day.
Ooh there it changes everything :!:
This is what we risk when we do not give all the information ...

Under these conditions, the consumption will be much more important than to "simply" keep the freezer at -20 ° C. :!:

In terms of energy:
  • cool 1 liter of liquid water from 30 ° to 0 ° = 4185 * 30 = 125550 34,875 J = XNUMX Wh
  • freeze 1 liter of water at 0 ° = 334000 J = 92,778 Wh
  • cool 1 kg of ice from 0 ° to -20 ° = 2060 * 20 = 41200 J = 11,444 Wh
Total: 140 Wh per kg of ice.

Producing 100 kg of ice per day (provided that the freezer is capable of operating without stopping, which would surprise me) therefore requires a thermal energy of 14 kWh.

Assuming that the freezer's COP is 2 (this is optimistic with a high ambient temperature), it will therefore require an electrical consumption of 7 kWh without counting the losses (which can be estimated at 1,3 kWh / day of after the information in the first post), i.e. in total an electrical consumption of almost 9 kWh per day.

Which requires completely reviewing the sizing of batteries and photovoltaic panels :!:
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Re: Help sizing freezer Steca PF 240




by kau » 27/04/16, 20:31

From this point of view, I will have to lower my ambitions. Even if in my 1st calculations, the return on investment occurred after a year, but that was before your interventions. But hey, I will not give up.
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Re: Help sizing freezer Steca PF 240




by chatelot16 » 27/04/16, 22:49

a domestic freezer, it is made to preserve already frozen product, is just occasionally freeze some products

if you want to make a large quantity of ice to sell it you need a refrigerating machine calculated for! an ordinary freezer is not enough

the cooling capacity will have to be quite strong, the quality of insulation is unimportant ... unlike the conservative freezer where we neglect the cooling capacity to favor the quality of insulation
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Re: Help sizing freezer Steca PF 240




by chatelot16 » 27/04/16, 22:55

if the goal is just to make ice no need for a battery ... you need a powerful refrigeration machine powered directly by the photovoltaic ... the more the sun makes electricity the more it makes ice ... we do not store not the electricity in a battery we store the ice!
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Re: Help sizing freezer Steca PF 240




by chatelot16 » 30/04/16, 20:50

commercially available mppt are made to optimize the charge of a battery with a photovoltaic panel

to make ice without battery you need a completely special mppt inverter which does not make 50 Hz but a variable frequency to turn the refrigeration compressor just at the right speed to use the available photovoltaic power

I can't be the first and only one to have this idea! but how do you find out if such an inverter already exists?
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