Green Building Forum - Energy saving fridges and freezers

Energy saving fridges and freezers

GaryB — Sun, 04 Nov 2012 09:20:11 +0000

This summer I checked the energy consumption of my old larder freezer and was shocked to find it was consuming > 2 kWh per DAY. This is equivalent to 750 kWh pa, costing me Â£115 a year.

I insulated the freezer sides and top (it had a condenser coil at the back) but it didn't make a noticeable difference. No longer requiring the capacity of freezer (due to empty nest syndrome), I ordered a frost free fridge freezer rated at 226kWh pa.

This new unit has been running for just over a week and the plug-in meter indicates it used just 1.74 kWh over a week.

The energy consumption equates to just 90 kWh pa, much lower than the 226 kWh pa official rating. This performance is I believe down to the following:

The fridge freezer is in an unheated utility room (10 deg C to 15.5 deg C range) giving less heat gain, but because it is primarily a fridge, the official rating must include for frequent opening and closing of the door, which doesn't happen as it is used as an overflow for our Bosch larder fridge (113 kWh pa).

The fridge freezer cost just Â£219.00 including home delivery. This gives a payback of 2 years and will save 650 kWh pa of leccy.

I recommend checking of your existing equipment using a plug-in meter and also reduce the amount of times the fridge door is opened and closed, as this seems to have quite an impact on consumption.

Energy saving fridges and freezers

SteamyTea — Sun, 04 Nov 2012 09:48:28 +0000

Just for a giggle and if there is some spare room in the fridge, put a couple of buckets of cold water in it and see if the energy use goes down after it has settled.

I found insulating the sided of mine helped, though that could be because it was a 100 quid one.

Energy saving fridges and freezers

GaryB — Sun, 04 Nov 2012 10:23:17 +0000

This new one has the heat rejection via the side panels - they run at around 25 deg C when the compressor is operating.

There were about 40 cans and bottles in it during the week - approx. 13.5 litres = 3 gallon buckets, so already done. Perhaps I should run it empty for a week to compare? The rules seem to be to keep a freezer at least 75% full but to leave plenty of circulation space in the fridge.

Energy saving fridges and freezers

fostertom — Sun, 04 Nov 2012 10:42:07 +0000

Posted By: GaryBThe rules seem to be to keep a freezer at least 75% full

Why is that ? I never understood that.

Energy saving fridges and freezers

GaryB — Sun, 04 Nov 2012 10:45:34 +0000

Tom, I believe it is a straightforward case of thermal mass reducing compressor cycling. However, I can't get to grips with the opposite logic for fridges...

Energy saving fridges and freezers

Ed Davies — Sun, 04 Nov 2012 12:11:45 +0000

My understanding is that it's about reducing the air change effect when the door is opened. Probably a mixture of reasons.

Energy saving fridges and freezers

fostertom — Sun, 04 Nov 2012 12:32:02 +0000

Sure it's not that the m/c consumes x amount of elect, so the fuller it is the less elect per item, therefore - faulty conclusion - it works more economically when filled up (with any old thing)?

Energy saving fridges and freezers

Simon Still — Sun, 04 Nov 2012 13:17:10 +0000

Posted By: Ed DaviesMy understanding is that it's about reducing the air change effect when the door is opened. Probably a mixture of reasons.

pretty sure it's this as the recommendation I'd heard was to fill with empty space in the freezer with newspaper rather than, say, ice cream tubs full of water. My assumption was that you're trying to minimise the amount of warm, wet, air entering when you open the door.

Energy saving fridges and freezers

Seret — Sun, 04 Nov 2012 15:21:10 +0000

Posted By: Ed DaviesMy understanding is that it's about reducing the air change effect when the door is opened. Probably a mixture of reasons.

Yup.

Energy saving fridges and freezers

SteamyTea — Sun, 04 Nov 2012 17:32:04 +0000

I once filled my fridge full of 'cheap euro beir' when I can home once, the compressor run for about an hour and a half then packed up and had to buy a new fridge, so maybe it is to stop drunken morons doing what I did . After the filth bottle of luke warm bier at 5% you don't care much

Energy saving fridges and freezers

HalcyonRichard — Mon, 05 Nov 2012 15:36:30 +0000

Hi,
I Replaced an old fridge freezer that was using about 2 kWh per day. The new one stated average use of about 1 kWh per day and was twice the size. Which was perfect as we freeze a lot of produce from the garden. By choosing an energy efficient one we save about Â£50 per year. As it cost Â£500 it will in effect pay for itself in about 10 years. Measured over one week when we were on holiday it was as close to 1 kWh per day as damit. Sadly most people go for the pretty one and don't care about efficiency.

Hi Steamy,
Have you considered home brew ? You could fill loads of fridges with it. Seriously It's fun to do and you can get 100's of different types and flavours of kits. It is also easy to modify the amount of water and sugar to make the perfect customised brew. You can also modify the second fermentation to give the perfect amount of "fizz". I have been doing it for about four years and always seem to run out. I don't know where it all goes

Richard

Energy saving fridges and freezers

rhamdu — Wed, 07 Nov 2012 20:25:33 +0000

I think the whole thing about keeping fridges/freezers 75% full is based on a misunderstanding.

If your fridge is almost empty, don't fill it up. Get a smaller fridge!

Energy saving fridges and freezers

GaryB — Sun, 11 Nov 2012 08:32:28 +0000

This week I monitored the fridge freezer with the fridge compartment virtually empty (as it's a 'reserve' fridge I can have it empty or full for testing purposes).

Consumption went up from 1.74 kWh to 1.92 kWh - a 10% increase. Door opening between the two periods was consistent, ie. door opened 3 times in the week and the freezer content remained stable.

I have lots of cans of soft drinks which have chilled overnight in the car so I will fill the fridge up again to see if the energy used reduces.

Energy saving fridges and freezers

SteamyTea — Sun, 11 Nov 2012 08:58:07 +0000

Was the ambient air temperature about the same?

Energy saving fridges and freezers

GaryB — Sun, 11 Nov 2012 12:24:01 +0000

Yes, indeed it was - I'm monitoring that too.

I'm following my old school science methodology of changing only one variable at a time (reinforced by extensive post-graduate research on fuel efficiency in 2 stroke petrol engines).

Energy saving fridges and freezers

SteamyTea — Sun, 11 Nov 2012 12:31:17 +0000

Posted By: GaryBI'm following my old school science methodology of changing only one variable at a time

The only way to do it. What I found so frustration with climate science, for virtually every variable there was another one that contracted it.

Do you know what happened to the STEP 2 stroke ICE?
Or for that matter the one that Ford started to put into Fiestas

Energy saving fridges and freezers

GaryB — Sun, 11 Nov 2012 14:43:44 +0000

ST:

I completed my research thesis in 1985 which pre-dates the developments you referred to.

The major problem for 2-strokes was not fuel efficiency (as the research into scavenging efficiency in the 70's and stratified charging in the early 80's was quite successful), but excessive emissions, particularly of lubrication oil transferred from the crankcase into the inlet transfer ports, hence the smoky blue exhaust fumes typical of two-stroke engines. Even feeding the oil directly into the crankcase couldn't stop this.

The diesel Fiesta is something of a celebrity in the classic car scene, see: http://www.fiestaguides.co.uk/phpBB2/viewtopic.php?t=6425&sid=13534ba8a55e852163aaf3ce1cb5ceb9

Energy saving fridges and freezers

SteamyTea — Sun, 11 Nov 2012 17:23:36 +0000

I had a Yamaha YDS3, I think that was one of the first autolubes available. Made a lot of noise, went faster than the Superdream and smoked more than I do.

I seem to remember that the STEP 2 Stroke had a conventionally lubricated crank and stepped pistons, the bottom half acting as an air pump and the top half as the combustion chamber. Looked a good idea on paper. I personally Galway liked the rotary engine, pulled on apart in 1981 at the start of my Auto Engineering course, coudl not get it back together in 1983, suspect it is still sitting in a box somewhere in Poole and Bournemouth college

Energy saving fridges and freezers

GaryB — Sun, 11 Nov 2012 18:09:54 +0000

A bit of a deviation into petrol head territory, last post off topic...

My test rig engine was based on a single cylinder 400 cc Yamaha from a DT400 connected to a brake dynamometer mounted on a 2.0 tonne cast iron bed on a vibration isolated concrete raft. Before testing and while I was programming the CNC milling machine for the manufacture of the cylinder head, the ICE Lab Technician was mounting the cast iron bedplate.

Once everything was connected up, I started preliminary testing using a tuned racing exhaust matched to the engine. Got up to 4,000 rpm with no issues, then looked over at the test rig as the engine came on tune, to see the test rig on its bedplate moving across the floor!

Turns out the Lab Technician couldn't be bothered moving the bed to bolt it to the concrete raft and just dropped short M12 bolts into the holes, he thought that the 2 tonne weight would be enough to hold it...

Energy saving fridges and freezers

rhamdu — Sun, 11 Nov 2012 18:42:08 +0000

Meanwhile back in the kitchen...

How the hell do you keep a fridge 75% full without shopping every day? (I'm assuming this is a fridge used for preserving food, not just cooling the next six cans of beer.)

And have you allowed for the fact that it is harder to find stuff in a full fridge, so the door is likely to be open for longer?

Energy saving fridges and freezers

SteamyTea — Sun, 11 Nov 2012 18:46:11 +0000

Posted By: rhamduHow the hell do you keep a fridge 75% full without shopping every day?

My lodger manages it, goes and buys stuff, forgets it in there, then goes and gets a takeaway.
I point out that it it cheaper for her to just buy a takeaway and use the fridge just for milk. Though at 50p/pint it is probably worth just buying a bottle a day and binning it.
It is strange how we worry over a fraction of a kWh/day and then chuck out food. I find tinned and dried stuff excellent.

Energy saving fridges and freezers

SteamyTea — Sun, 11 Nov 2012 18:47:24 +0000

I think I have found out how to make text invisible

put a < in there at the beginning of the line

Energy saving fridges and freezers

rhamdu — Sun, 11 Nov 2012 19:14:38 +0000

An Indian friend told me that when she was young they didn't even have a fridge!

Nor us, I said. In the moment's silence that followed, I asked: so how did you keep the milk fresh in India?

'We boiled it twice a day.'

Energy saving fridges and freezers

GaryB — Sun, 11 Nov 2012 20:47:53 +0000

Posted By: rhamdu

How the hell do you keep a fridge 75% full without shopping every day?

The 75% rule applies only to freezers, the conventional wisdom in respect of fridges is to keep them less filled. My fridge freezer energy readings are atypical as the fridge door is rarely opened. Interestingly, my fridge freezer is only consuming 37% of its certified energy - door opening appears to have quite an impact on consumption.

Energy saving fridges and freezers

rhamdu — Sun, 11 Nov 2012 21:15:44 +0000

Anyone tried one of those 'drawer' fridges?

Posted By: GaryBThe 75% rule applies only to freezers, the conventional wisdom in respect of fridges is to keep them less filled.

Thanks Gary - any idea on what the conventional wisdom is based?

Energy saving fridges and freezers

GaryB — Sun, 11 Nov 2012 21:17:04 +0000

No - I can't figure it out myself!