Energy conservation

Status
Not open for further replies.
gar said:
On the freezer I am currently testing the on period is about 44% (164/370) of the total cycle time. An experiment I will run later will be with about 4" of foam insulation around the outside of the cabinet. This experiment should show a substantial change.

Assuming no air leakage the heat loss from an enclosure in still air is a function of the outside surface area and the thermal resistance to the interior. The thermal resistance is determined by the insulation between the outside surface and the interior. A typical calculus question is what rectangular shape box has the least surface area to interior volume? This shape is a cube.
Click to expand...

Watch out! I inadvertently tried that experiment, with undesirable results.

I have a freezer in a storage space, and I had a few pieces of foam plank insulation to store. Thinking that a little extra insulation couldn't hurt, I simply propped the foam up on the side of the freezer.

Some months later, I decided to feel under the foam. The side of the freezer was _hot_.

I then went found the freezer manual online, and the installation instructions require clear space all around the unit for air flow.

I don't know what the heat source is; my guesses are: 1) heaters to prevent condensation 2) condenser coils integrated into the outer surface to get more area with which to reject heat 3) heat conducted by the metal walls from the compressor or condenser. In any case, the added insulation acted to retain the heat generated by the freezer, presumably lowering efficiency.

Some additional info: this is an upright freezer, and the back of the freezer does not have an exposed condenser coil. Compressor is apparently at the bottom, but with no apparent fan or significant air flow.

-Jon
 
090730-1930 EST

winnie:

The upright freezer I was currently testing has cool sides and front. On the rear side is the condensing coil.

My other upright has warm sides. Not sure if there are any coils on the back side. My side-by-side GE refrigerator has the condensing coils at the bottom.

Both these are being moved to the other side of the garage and at that time I will determine more information on the units and run more tests.

I was really disappointed today when I ran the voltage range check on the "Kill A Watt" meter.

.
 
Besoeker said:
The heat you extract from the stuff you freeze has to somewhere.
Preventing it from doing so is not such a good idea.
Click to expand...

Oh, I know this full well.

What I didn't know, and didn't think to check was _where_ the hot side of this particular heat pump would be. I'd just _ass_u_me_d that the condenser coils would be on the back, and that the sides were just blank insulated panels. Whoops.

-Jon
 
weressl said:
You know I never got that. Why do YOU have to sleep in the couch when it is HER who does not want to sleep in the same bed?:roll:
Click to expand...

And I've never let this happen to me. We either stay up late to work it out or she can turn her back. Its MY bed too! :roll:

Happily this hasn't been an issue in years...
 
winnie - since it was a freezer, if it is a frost-free freezer you just happened to feel it when the heating coils in the walls were on. They cycle on once in a while to melt and evaporate anything on the walls inside. I bet if you felt it another time it would be cold.

Most fridge/freezer combos have this on the freezer compartment, and similar coils on the outside of the fridge compartment for condensation control. Sometimes there is a switch inside to turn the condensation control off - great for saving some energy.
 
techntrek said:
winnie - since it was a freezer, if it is a frost-free freezer you just happened to feel it when the heating coils in the walls were on. They cycle on once in a while to melt and evaporate anything on the walls inside. I bet if you felt it another time it would be cold.
Click to expand...

To be clear, I understand the thermodynamics of freezers and heat pumps...but I've clearly demonstrated that I don't understand the mechanics of freezers as they are actually manufactured.

I'm pretty sure that this was not a frost free unit; I know that I have to manually defrost about 1-2x per year. Additionally, the frost accumulates on the shelves, which double as the evaporator (cold) coils. No frost accumulates on the walls.

But what I really don't get is why frost removal heating coils would be on the _outside_ of the freezer.

My best _guess_ is that the condenser (hot) coils are integrated with the outside case of the freezer, to use the chassis itself as the heat radiator. I would love confirmation or correction on this point.

-Jon
 
Meter Reading

Meter Reading

When I asked about how to read calculate the meter readings I was refering to the meter on the side of my house how to read the dials?
 
090731-1650 EST

Mike01:

On my outside KWH meter I have 5 dials. These indicate the cumulative KWH. The current reading from left to right is between 1 and 2, this is a 1; next between 3 and 4, that is 3; 3rd dial is at 7, thus 7; next between 0 and 1, so it is 0; and the right most between 2 and 3, read as 2.5. The accumulated number is 13702.5 .

My disk took about 19 seconds for one revolution. My TED unit read 2.41 KW.

.
 
winnie said:
My best _guess_ is that the condenser (hot) coils are integrated with the outside case of the freezer, to use the chassis itself as the heat radiator. I would love confirmation or correction on this point.

-Jon
Click to expand...
It would seem odd to essentially wrap your freezer with heat tape. You usually try to get the coil away from the cold area. Somebody must have a exploded parts diagram somewhere. Sears has that kind of stuff online. If I remember, I'll try to look later unless someone else feels froggy.
 
090801-0809 EST

Mike01:

The meter reads modulo 100,000. This means the number system consists of the integers 0 thru 99,999, and adding 1 to 99,999 = 0. In a number system modulo 100,000 if I input the number 389,123 the result will be 89,123.

Sometimes this is called clock arithmetic. In the case of a normal clock you have the integers 1 thru 12. So military time of 1320 corresponds to 1 PM and 20 minutes.

If you make a binary counter of 10 bits, then it has a range of 0 thru 11111 11111. In decimal this translates to 0 thru 1023. Thus, it is a modulo 1024 counter. When 1 is added to 1023 the result is 0. If 10 was added to 1023 it would equal 9. If 11 is subtracted from 9 the result is 1022.

.
 
gar said:
090801-0835 EST

mivey:

At
http://www.fridgerepairs.com.au/tips.htm

in the second paragraph after the "On Holidays" heading there is mention of condenser coils welded to the inside of some cabinets.

.
Click to expand...
But does not indicate they use the cabinet for a heat exchanger. If that were the case, I would think the coils would wrap around to make the best use of the available surface area.

This chest freezer diagram shows the coils on the back only:
http://www.searspartsdirect.com/par...CABINET&documentId=00023266&backToLink=Return

This upright also has the heat exchanger in the back only:
http://www.searspartsdirect.com/par...=SYSTEM&documentId=10043375&backToLink=Return

My wife's uncle is an appliance repairman. I'll try to remember to ask him next time I see him as he will have seen many styles.
 
mivey said:
But does not indicate they use the cabinet for a heat exchanger.
Click to expand...

That would be kinda silly if you think of it. Injecting the same 'heat' you just removed from the inside of the fridge/freezer?

As the article quoted by gar indicates - although not clearly - SOME of the exchanger coils are taken inside of the cold area to dehumidify the air inside.

The same happens in your whole house HVAC unit too. So the dehumidification takes extra energy though, yet returns some because it takes more energy to cool moist air.
 
I just got notice that my TED 5000 shipped today - looking forward to playing around with it. I have a wireless router/switch and outlet next to the panel, so the power line communication with the gateway unit should be very short and reliable, going then through wired enet and then wireless to the rest of the house. I skipped the zigbee wireless display unit, deciding to go just with the computer access. The http interface looks very easy to interface to custom applications/scripts.
 
091107-1602 EST

I have been running some test on freezers.

One test has been on the cost of freezing a given quantity of a substance. The experiment is with water. The current test is with 5# of water. or about 5/8 gallon.

5# of water is about 2268 grams. The specific heat of water is about 4.2 joules per gram per deg C in liquid form above freezing. Below freezing ice is about 2.09 joules per gram per deg C. The heat of fusion is about 333.7 joules per gram under standard conditions.

My water started at 52 deg F and the test ended at + 7 deg F.
From 52 deg to 32 deg should take 105734 joules.
From just above 32 to just below 32 should take 756831 joules.
From 32 to 7 should take about 65888 joules.

Note one joule = one watt-sec.

Thus, for the three states I need 29 + 210 + 18.3 = 257 watt-hours. Did I make any mistakes?

Over this test period the ambient temperature of the air around the freezer was 55 to 56 deg F. The total time of cooling the water from 52 F to 7 F was 25.367 hours and the total watt-hours were 3570, or an average power of 140.7 W. The base average power under the same ambient conditions is about 130 W. Thus, about 10 W average was required to cool the water. And this calculates to 254 watt-hours.

A close correlation, but the actual energy consumed should be moderately higher than the calculated required energy because of the inefficiency of the refrigeration system.

My experimental setup has a major problem. The time to perform the experiment is too long because all the water is in one plastic jug and the heat transfer rate is slow. This does not provide a high enough load on the refrigeration system to have much effect on the heat cool-duty cycle. In the future if I rerun the experiment I need more water being frozen and in separate conductive containers. For example, maybe 20 # of water in 10 different conductive containers, and all containers in contact with the shelves.

I have two freezers with which I am experimenting. Neither has fan.

A significant conclusion is --- if the weather outside is below freezing, then you should prefreeze outdoors anything that is to go into the freezer before putting it into the freezer. It does not take the experiment or calculations to conclude this because it should be self-evident from apriori knowledge from physics and chemistry classes. The experiment and calculations are a nice confirmation.

It is also important to note that for this particular freezer that the average power loss at an ambient of about 55 deg F is 130 W or 1139 KWH/year and at my current rate about 1139*0.133 = $152.

.
 
Status
Not open for further replies.
Top