Pimp my Husky / Eliwell ID961plus

[BrianFWombat]

Firstly, apologies for such a newbie and amateur question... hopefully it is obscure enough to be of some interest...

I have purchased a second hand Husky Coolcube drinks chiller with the intention of making it into a stable hibernation environment for some reptiles. The goal is to be a stable 2 to 5 celcius; freezing would be a disaster so the unit as a whole cannot fall to zero or below (including any over-run)

I have eliminated the existing thermostat and am driving the compressor directly using a ID961 controller with a probe in the main compartment. It seems OK although the temperatures fall significantly after compressor turn off.

The Husky chiller is very simple; it has a fan less evaporator with no defrost sensing or element so free defrost is my only option.

The default for the ID961plus seem to be a defrost every 6 hours with a free defrost of 30 mins. To me this defrost cycle seems too frequent and not helpful for my desire to maintain stable temperatures for the animals involved.

I am considering changing dCt to 0 (from default 1) and increasing dit to 10, leaving dEt at 30.

Any advice?

Thanks in advance
Brian

[sedgy]

hi brian, you say the temp drops after the comp drops out. do you have the evap fan off also? this could be cooling after the comp , drops out,
hope you dont freeze this winter, sedgy,

[BrianFWombat]

Sedgy,

This chiller is really simple... no fans at all, just the compressor. The chiller is just a box, intended for holding cans of beer. It has an upper section with an evaporator (no fan) and a lower section split by a rack. The lower section is only half the depth of the cube, the compressor being housed in the gap at the back.

With the compressor running the evaporator gets very cold, which is good. What I was refering to is the fact that once the Eliwell has turned the compressor off the temperature will continue to drop for a bit; I think this is to be expected since there is not a huge thermal mass inside the fridge and the evaporator is at this point very cold, a very cold chunk of metal at sub-zero.

I'm particularly concerned about creating a proper defrost regieme since I would like the fridge to operate unattended for a few months. At around 10C the inhabitants will start to wake up so I need to keep the temps always less than 8C or so but at the same time I do not want ice building up on the evaporator. The contents cannot be allowed to go to 0C as this will cause irreparable central nervous system damage to the inhabitants.

I'm not quite sure what dCt=0 means but I feel that it is more appropriate than dCt=1.

Regards
BfW

[chemi-cool]

here is the controller manual.

Read it carefuly and see how it works.

[BrianFWombat]

Thanks but I already have the ID961 manual and also the ID961plus manual which is very similar.

The manual shows...

dCt
0 = compressor operating hours (DIGIFROST® method);
1 = Real Time – appliance operating time;
2 = compressor stop.

dCt=1 is the default.

My question was under what circumstances dCt=0 would be more appropriate and if and dit=10 dEt=30 were appropriate values.

The manual has no application notes on the use of dCt; I was interested in the views of those who used this controller, or similar ones in practice.

I would also be interested in why dCt=1 is the default.... isn't dCt=0 a much more sensible option?

Thanks
BfW

[frank]

If you want to guarantee that the unit doesn't continue to cool after thermostat off then you need to convert it to pump down control.

Might be a little outside of your capabilities. although a good local engineer could easily do the work for you.

[Gary]

The goal is to be a stable 2 to 5 celcius; freezing would be a disaster so the unit as a whole cannot fall to zero or below (including any over-run)

What are your humidity requirements, if any?

[Andy AC]

My husky ain't man enough to keep my beer cool for more than a couple of days - I fear for your reptiles.

Andy

[BrianFWombat]

What are your humidity requirements, if any?

Around 50-60%

[BrianFWombat]

My husky ain't man enough to keep my beer cool for more than a couple of days - I fear for your reptiles.

Andy

That was my initial thought too; in fact I expected to bin it almost immediately but it does seem to cool quite effectively at the moment probably because ambient is around 18C. I imagine that in summer it might not be able to cope. I had intended to switch to a larder fridge but the Husky seems to be working and it is nice and small so fits in a gap in the hallway; we don't really have space for a full fridge inside and temps cannot be guaranteed outside.

[BrianFWombat]

If you want to guarantee that the unit doesn't continue to cool after thermostat off then you need to convert it to pump down control.

Might be a little outside of your capabilities. although a good local engineer could easily do the work for you.

Well beyond my capabilities!

[Gary]

I would attach the temp control sensor to the suction line at the coil outlet, then set the control to start at 5C and stop at -2C. The air flowing over a -2C coil should be above freezing and the coil should be defrosted at 5C.

[BrianFWombat]

I would attach the temp control sensor to the suction line at the coil outlet, then set the control to start at 5C and stop at -2C. The air flowing over a -2C coil should be above freezing and the coil should be defrosted at 5C.

That's an interesting idea. So the setpoint would be -2 and the dif +7

The other idea I am considering is adding an evaporator fan, this could maybe tend to equalise the temperatures and make the heat capacity of the evaporator less of an issue. The temps in the fridge are quite different at present... the lower section is around 3C warmer than the top. Present readings are 3.8C at the top 6.6C at the bottom. Adding further control for a fan and additional probe mean I also need to move to another controller... probably ID971 so more expense but quite fun; not sure if the Husky merits such attention.

[BrianFWombat]

After a bit of thought I have decided that the temperature differential is next challenge so I think I will fit a fan (in a cowling) to circulate the air from the top past the evaporator and out towards the bottom. Given my current ID961 controller does not have fan control I will just make this slow running but permanently on, using a 12v computer fan with cheap controller and see what happens.

[BrianFWombat]

I have added a cardboard section at the back of the fridge, it comprises a vertical wall 15cm high with holes at the bottom and a sloped section approx 10cm that is angled into the main compartment and joins the ceiling. In the sloped section I have a fan that draws air in. The arrangement is placed in front of the evaporator just in front of the drainage gully, i.e. there is approx a 4cm gap for air flow. The fan is running at a moderate speed and is continously running.

Adding this arrangement has dramatically increased the temperature uniformity of the contents, there is now less than 1C temperature gradient between top, middle and bottom of the unit and the swings in temperature seem to have decreased.

I am thinking of reducing dif to 0.5C but am aware this will cause more compressor cycles...

What sort of duty cycle should be expected in a fridge? (At the moment the compressor is off for long periods, but when turned on the temperature drops from set+dif to about set-2.0C, reducing dif should help??)

Thanks in advance
BfW

[BrianFWombat]

And another, maybe a better question... How many compressor starts per hour should I be aiming for?

Thanks again,
BfW

[BrianFWombat]

On another thread I found....

rule of thumb 6-8 starts per hour

[Gary]

Where are you measuring that set -2C?

Are you sensing return air, supply air, pipe temp?

What are your return air and supply air temps?

[Gary]

You seem to think it's all about temperature. It's about temperature AND humidity.

If humidity doesn't matter, then we can simply sense return air and go for maximum cycles (6-8 per hour).

If humidity matters, which I suspect it does, then the ideal sensing point would be the center of the coil and we need to spread the differential to remove the optimum amount of moisture. The higher the differential, the drier the environment and vice versa.

[BrianFWombat]

You seem to think it's all about temperature. It's about temperature AND humidity.

Gary, Apologies...

I have almost no knowledge about this field apart from my school physics lessons so I don't really understand that statement.

The temperatures I am measuring are with probes in one of the two storage boxes within the fridge. Measured humidity is around 50% inside the fridge at around 5C.

My goal is to keep the contents of the fridge at as close to 5C as possible for the next 3 months; but at all costs to avoid the contents ever going to 0C.

5+/-1 degree C would be a great outcome.

Currently I do not seem to be having any significant build up of frost on the evaporator so defrosting doesn't seem to be an issue at all. I put this down to better regulation of the compressor now I am using a ID961plus controller??

Regards
BfW

[Gary]

No need for apologies.

The higher the differential, the colder the coil gets and the more moisture is removed from the air. Then when the temp swings back upwards on the off cycle, the humidity swings downwards to a lower level due to the reduced moisture content in the air.

But if you are achieving 5C@50%RH, this sounds like the target you were aiming for.

Is the system short cycling (more than 6-8 cycles per hour)?

[Gary]

Living creatures are sensitive to both temperature and humidity, humans being most comfortable and healthiest between 40-60%RH. I have no idea what the healthiest RH is for reptiles in hibernation, which is why I enquired earlier.

[BrianFWombat]

Current humidity is now 60. Target for the animals is 50-60 so this is OK.

I have the controller set to SET 5.2 and DIF 0.5

Last night I added a probe (Pt100) into the middle of the compartment and left my rather primitive data logger running (ADC in Multimeter attached to a PC)... the results were...

Temperature range seems to reliably be in cycles between 3.8C and 6.6C; the shape of these cycles is a sawtooth. From minimum temperature 3.8C the contents slowly warm up to 6.6C over a time which is reliably around 840seconds... i.e. 14 minutes exactly.
Once at a high point the temperature declines more rapidly to return to the minimum temperature in 305seconds, i.e. 5 mins.

The system is therefore on a cycle with period 19 mins, i.e. around 3 per hour.

I guess I could reduce dif even further?

How many minutes in any 60 would a compressor be expected to run? I guess at the moment it is on for 15.

Thanks
Gavin

[BrianFWombat]

I just measured the compressor run time... with the current configuration the compressor runs for approx 3.5 minutes in each cycle. i.e. runs for 3.5x3=10mins per hour.

Does having more frequent cycles make sense in this scenario? (They would have to be very short).

[Gary]

If you further reduce the diffferential, the humidity will go above 60%.

I would declare it a big success and go celebrate.

[BrianFWombat]

If you further reduce the diffferential, the humidity will go above 60%.

I would declare it a big success and go celebrate.

Thanks! I would celebrate with a chilled beer but unfortunately the tortoises are in the fridge.

Regards
BfW