saving energy

[cadwaladr]

i am going to fit timer to a clients cold store so it only runs on cheap rate electric its a cold store/holding room running at minus 25c ,going to put it in the control ,adjust the defrost so it only defrosts at night,not much traffic into room in peak the product is meat input temp is minus 18,can anyone forsee a problem?

[mad fridgie]

This is a very interesting question, I too, a long time back looked at a solution like this (if i have understood it correctly)
It was my intention to overshoot the temp at night (lower SCT and electricity prices) a double saving.
Luckily at the same time i was working with some food scientists, study long term food storage.
This temperure swing method was researched. It was found that the internal structure of the meat became damaged and also at cellular level becamer drier.
A bit more detail!
The varing temps changed the internal water vapor pressure (causing water vaporization) and continues expansion and contraction of the meat further damaged the cell walls (which happens in the freeze process as standard).
It is best for the product to keep a contant.
I will let you make up your mind, which is more important product or energy saving!

[cadwaladr]

i thnk thats good advice thanks,talked to customer today and we decided to adjust temp to keep store at -18c not -24,and to defrost the coils at night,will install my comark data logger for a week to get data thanks again.

[US Iceman]

This is a very interesting question, I too, a long time back looked at a solution like this (if i have understood it correctly)
It was my intention to overshoot the temp at night (lower SCT and electricity prices) a double saving.
Luckily at the same time i was working with some food scientists, study long term food storage.
This temperure swing method was researched. It was found that the internal structure of the meat became damaged and also at cellular level becamer drier.
A bit more detail!
The varing temps changed the internal water vapor pressure (causing water vaporization) and continues expansion and contraction of the meat further damaged the cell walls (which happens in the freeze process as standard).
It is best for the product to keep a contant.
I will let you make up your mind, which is more important product or energy saving!

Good advice here. Sometimes what we might do can cause harm to the food stored. Some products will tolerate a small temperature excursion while others are intolerant of small temperature swings.

[cadwaladr]

i suppose widening the diff could be a better idea,cut out -20c cut in -15c by the way fans run in the off cycle.The product being stored is donner kebabs and chips /beefburgers,so the advice via the scientists is relavent.

[mad fridgie]

i suppose widening the diff could be a better idea,cut out -20c cut in -15c by the way fans run in the off cycle.The product being stored is donner kebabs and chips /beefburgers,so the advice via the scientists is relavent.
If we take your product and look who going to eat it and when (after a skinfull of beer), cell structure quality is not so important (compared to a steak), Increasing the diff is changing the product temp, so same rules apply.
How big is the store, if smallish then heat infiltration will change the air temp quick, but if large with lots of product, then thermal mass comes into it.

[Magoo]

Try cycling evap fans when store is at normal temp condition, if store is reasonably full the compressor cycling/operational time is dramatically reduced. Perhaps pulse start fans on every 15 minutes in off cycle for say a minute to stur up air in store.
With low activity overnight, the only input heat is structure gain and fan HP gain.
I have done this on a couple of stores with reduction in power usage. The mass of product temp won't change. But you have to have store reasonably full of product.

[fridge doctor]

I am assuming cheap rate electricity to be at night - typically 24-00 thru 07-00am? That being the case, and aagain assuming the coldstore is 'closed for business' during these hours. You should insert the timer so that EVERYTHING stays off for that period - especially the defrost which apart from using more power than refrigeration, will also push heat into the room - definitely a no-no!

You should install a second thermostat and place the phial/sensor into a container. The container you choose will probably be metal and have a screw cap. Pierce the cap and place the sensor in the middle of the container which you fill with water, and position in a mid range location in the coldstore out of harms way and protected by a metal guard.
The wiring of the thermostat will be introduced to the system in such a way as to override the 8 hour shut down only IF & WHEN a pre-determined core temperature is exceeded.

[cadwaladr]

I am assuming cheap rate electricity to be at night - typically 24-00 thru 07-00am? That being the case, and aagain assuming the coldstore is 'closed for business' during these hours. You should insert the timer so that EVERYTHING stays off for that period - especially the defrost which apart from using more power than refrigeration, will also push heat into the room - definitely a no-no!

You should install a second thermostat and place the phial/sensor into a container. The container you choose will probably be metal and have a screw cap. Pierce the cap and place the sensor in the middle of the container which you fill with water, and position in a mid range location in the coldstore out of harms way and protected by a metal guard.
The wiring of the thermostat will be introduced to the system in such a way as to override the 8 hour shut down only IF & WHEN a pre-determined core temperature is exceeded.this store is 7mtrs square 2.5mtrs high,it holds about25 pallets,mixed goods chips donner kebabs,but there is not a lot of traffic/entries 2hours per day ambient is 10 degrees c
8amthru 12 am,however freshly made donners are introduced to freeze down.maybe it would be efficient to have two stats night/day but to run colder at cheap rate[night 11pm/6am?

[charlie n]

Operating with two air temperatures over a range of -18 to -22 or -23 will not damage the product. I suggest you run at -24 at night when the power is cheap and -18 during the higher cost time. Cycle the evaporator fans the same as the liquid solenoid on thermostat but turn them on for 5 minutes every 1/2 hour like magoo suggests.

[cadwaladr]

Operating with two air temperatures over a range of -18 to -22 or -23 will not damage the product. I suggest you run at -24 at night when the power is cheap and -18 during the higher cost time. Cycle the evaporator fans the same as the liquid solenoid on thermostat but turn them on for 5 minutes every 1/2 hour like magoo suggests.good advice that was what i thought the best,the only prob is cycling the fans its not the most modern control panels delay timers are on fan circuit for post defrost purposes,do you mean put cycling timer in the fan circuit when in null mode?

[charlie n]

When the room thermostat is satisfied, it should close the liquid solenoid and also stop the evaporator fans. If the fans & solenoid are off for some time (about 30 minutes) a clock/timer should power the fans only for 5 minutes to move some air around and equalize the room temperature.
You could also try to connect the defrost clock into this circuit. This way the clock only runs when the liquid solenoid is open. The defrost cycle is then operated based on a certain number of operating hours which is more efficient than simply defrosting a certain time each day. If it's not cooling, it's not building frost so it doesn't need defrosting.

[fridge doctor]

Good proposal Charlie N, I like that. He could use a 'delay on' timer/relay for the fan control....

Take a pencil and draw this out :

Layout your existing components - solenoid, evap fans, evap fan contactor, heaters, thermostat and timer, and pencil in the live only connections between them all. Then introduce two new items a '5 amp double pole relay', and a similar sized 'Delay on relay/timer'. Now, interrupt the timer motor supply line and pass it through the normally open contacts of the new DP relay. Then pick up a supply from the output side of the thermostat (live when calling), and take this new supply to the coil of the new DP relay. So the coil is energised during 'on cycle' and operations now are as normal except that the timer motor stops when the thermostat is satisfied. Now use the NC side of the new DP relay to power the coil of your 'on delay relay/timer' and set it for 30 mins. Obviously you must then pass the fan supply (which is hopefully the coil of a fan contactor - if not you may have to fit one in the circuit), through the contacts of the 'delay on relay'.

So when the thermostat stops, power is broken to the timer motor, but directed to the 'on delay' relay, which then cycles the fans after c.30 mins. The problem is it would be difficult to minmise the running of the fans to say 5 minutes because it would require a further delay timer. I think that in most cases you could safely leave the fans on at this stage... a little experimentation with typical 'off times' of the plant, would give you a good idea where to aim on timing.

When the stat does come back into circuit, the DP relay reverts to NO and the On delay timer re-sets itself for the next period.

This is a basic set-up and will obviously need to be adapted to your circuit, particularly in respect of ensuring that the fans are able to operate normally in refrigeration mode. Let's assume for example that the fans (or fan contactor coil) is fed from the refrigeration side of the defrost timer. In such a case, locate the live supply INTO the timer, and pass this through the contacts of the on delay timer. In this way it can supply power to the fan (Contactor coil) even though the timer itself is temporarily inoperable. And because the relay contacts will open at the same time the thermostat closes, there will be no circuitry problems.

Hope that helps,

Trevor

[cadwaladr]

thanks to all for the advice,not yet had time to do any alterations to this system,i will post when i do the advicefrom fridge doctor is way i will adopt,need to balance,outlay and time,product safety.

[freezetech]

is this alteration just to save energy and money if so there are other ways
witout affecting you product

[cadwaladr]

is this alteration just to save energy and money if so there are other ways
witout affecting you productthis all started with the client asked why is the plant running so much,the evap fans run all the time but not on defrost,his energy bill is high.There is no problem with his product.Iam the guy who maintains the plant so felt obliged to help in any way i could,but i dont want to fit kit that would save him money but cost a lot to fit,the lower rate [night rate]was an obvious choice .the insulation is 100% strip curtains sensible use of door openings etc but this invoice from his electricity supplier is in his face,some of the donners enter at about +5c and be it only a small amount 60 /3 days a week keeping fans constant does affect there pull down,this production is in the day time thus leaving them in there with no airflow could and will harm the shape,but what do i do if the mods affect his end game ,so testing various ways is tricky,but some of the advice is good and the defrost on demand/alteration is what i will try first,as said in earlier post getting info thru data logger will be 1st step.

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[D.D.KORANNE]

What about variable frequency drive to save the enrgy . In any case the cold storage is not opened 24 hrs - 7 am ?