Fridge/freezer on Economy 7 possible energy-cost-saving trick?

RobM99

Lower wattage light in the fridge?

victor2

RobM99 said:

Lower wattage light in the fridge?

You do know the light is only on when the door is open? So we are led to believe anyway. 

devondiver

dunstonh said:

Samsung make one rated at 225kWh - 409L fridge / 226L freezer side-by-side.
https://ao.com/product/rs68a884cb1-samsung-series-8-american-fridge-freezer-black-94424-27.aspx

This is our model.   We bought it to replace one that was getting close to 3kWh a day.   We are now getting  0.74kWh a day.  

FWIW - my fridge/freezer (301L/111L over/under) is a several years old Bosch model rated at 175kWh/annum (bought nearly-new off ebay for £150!). When I monitored the power usage over 7 days recently it consumed equivalent of 165kW/annum (0.45kWh/day) - but, to be fair, we were away over the period so it didn't get opened much. I shall repeat the exercise for 'normal usage' in due course.

[Deleted User]

victor2 said:

RobM99 said:

Lower wattage light in the fridge?

You do know the light is only on when the door is open? So we are led to believe anyway. 

Have you ever managed to prove it though? 👀

devondiver

dunstonh said:

It is the biggest continuous-use item, although there are some very efficient F/F out there now (our American F/F uses 0.7kWh a day).     However, it is not necessarily the biggest single electrical use that a household will have.    Often that is either the dishwasher or the tumble drier.

Good points - but I suspect that most money-savers limit their use of dishwashers (I've never had one!) and tumble driers to less than once or twice a week - especially in the current climate. I certainly do .

BTW - please excuse my multiple posts. I've been away again and just catching up now.

[Deleted User]

Interesting thread, got me thinking as I do like the creative approaches to energy saving but there is another factor I'm trying to get my head around.

So a fridge/freezer is just a heat pump that moves heat from the inside to the outside, so when it is running it is adding heat to the room that it is in - AND all day long, heat from the room is slowly moving into the fridge through the casing which is in effect cooling the room slightly.

So all a fridge/freezer is doing is cyclic bursts of pumping heat absorbed from the room back out to the room. I get the principle that if it does more of the heat pumping during E7 hours it is cheaper, but you are stealing heat from the room during the day that you give back at night when you don't want heat in your room.

So going back to the OP's scenario, assuming they are on elec heating with the E7/10 meter.

1. Move the blocks into the fridge during the daytime, when the heating is on and therefore the room is warmer and therefore more heat moves into the fridge/freezer than during the E7 hours when the heating is off.
   
   
2. This heat moving into the fridge is not pumped back out because the freezer blocks absorb it, so the room heating will need to release a little more energy to keep at the same temperature.
   
   
3. But the freezer will now need a little more energy to stay at the same temperature because the heat energy entering the freezer will be absorbed by a smaller mass and therefore cause a bigger rise in temperature and a slight increase in energy used to pump that back out.
   
   
4. When night falls and the blocks are removed from the fridge and put in the freezer, all the heat from the room that they absorbed is now pumped back out of the freezer, warming the room slightly but at a time when you don't want any heating in the room.
   
   
5. So you needed to heat the room slightly more during the day to maintain temperature and then push that heat back out during the night when it wasn't needed.

Simplifying it, you are moving daytime heat from your room into ice blocks and then pumping it back out into the room during the night.

Can anyone help me here because it sounds like money saved by the fridge not heat pumping as much in the day is just offset by absorbing the energy used to heat the room and pumping it back out when you don't need it at night?

k_man

Isn't that only relevent when the kitchen/room is being, or needs, actively heated?

victor2

Does ALL the energy consumed by the fridge/freezer ultimately get released back into the room as heat? So, a fridge using say 1kWh per day gives out 1kWh of heat into the room? Presumably some of the energy consumed is effectively stored in the cold/frozen items?

Interesting argument @[Deleted User]. So the saving in electricity consumed at the cheaper off-peak rate compared to the peak rate has to more than offset the extra energy used to heat the room the fridge/freezer is in during the day? Assuming it is in a room you heat.

devondiver

Deleted_User said:

Can anyone help me here because it sounds like money saved by the fridge not heat pumping as much in the day is just offset by absorbing the energy used to heat the room and pumping it back out when you don't need it at night?

Seems logical enough - but there are many variables which may or may not be significant. I suspect the biggest question is:

How significant is the energy used by the fridge/freezer compared to the energy used keeping the room warm?

In my own case the f/f uses c.0.5kWh per 24h. My kitchen is heated by a single night storage heater which consumes between 0 and 20kWh per 24h (all cheap rate), plus cooker and appliances (including f/f) giving an average annual figure of say 10kWh/day. So 20 times more heat supplied to the room than that given out by the f/f.

And, although the storage heater heats up during the night and (theoretically at least) releases its heat to the room during the day, the room is always warmest during the day - aided by outside ambient temperature. And (again theoretically) any heat 'pumped out' by the fridge at night will offset the heat required by the thermostatically controlled storage heater. But again - the overriding questions are about the significance of any of these effects.

Any domestic energy thermodynamics aficionados out there? My brain is starting to hurt.   

dunstonh

devondiver said:

dunstonh said:

Samsung make one rated at 225kWh - 409L fridge / 226L freezer side-by-side.
https://ao.com/product/rs68a884cb1-samsung-series-8-american-fridge-freezer-black-94424-27.aspx

This is our model.   We bought it to replace one that was getting close to 3kWh a day.   We are now getting  0.74kWh a day.  

FWIW - my fridge/freezer (301L/111L over/under) is a several years old Bosch model rated at 175kWh/annum (bought nearly-new off ebay for £150!). When I monitored the power usage over 7 days recently it consumed equivalent of 165kW/annum (0.45kWh/day) - but, to be fair, we were away over the period so it didn't get opened much. I shall repeat the exercise for 'normal usage' in due course.

I didn't connect the ice maker initially and it was doing around 0.6kWh a day.  The ice maker added 0.1kWh per day.   That said, my daughter used to drink a 1.5litre evian per day but now uses the water/ice dispenser.   So, that was a nice saving!

Our old model was a cheapy beko.    It wasn't energy efficient to begin with and with American style F/Fs it is easy to buy cheap upfront but end up paying for it in the electric load.   That and the dishwasher were left behind by the previous homeowner for £50 and were only 2 years old at the time.  So, it effectively cost us nothing to buy them.

Good points - but I suspect that most money-savers limit their use of dishwashers (I've never had one!) and tumble driers to less than once or twice a week - especially in the current climate. I certainly do  .

I think those with families will be closer to once or twice a day.   We used to be twice a day on 65c.   However, we bought an extra dinner set and cutlery along with a modern dishwasher with a good eco programme.   It takes 4 hrs 55 mins for the eco wash but uses so much less electricity.  So, now it is only run once a day and during off-peak power.

When electricity is cheap, you don't think about being a money saver.   Now, the mindset of many people is changing and it isn't that difficult to change some habits to reduce your electricity use.    Whether I will feel the same way next year after our PV array is running, I don't know.   I probably will as I quite enjoy resource management, logging and trends etc.