Coldroom conversion r22 to r404a

Hi guys,

I have a customer who has a walkin coldroom running on r22 with a water cooled unit. He has been quoted some huge price to repair the water chiller.

I have suggested that he would be much smarter to change to a air cooled unit, something like a lil cubigel condensing unit and modern digital controls to better control temperature using it as a pump down system.

I have had a chat with a few other engineers who suggest I can keep the Evap and change the TEV for a r404a one and should get away with that. I do know that mineral oil and synth oil don't mix.

Not sure whether I should suggest replacing the blowers to be on the safe side, but there will be an extra cost

mineral oil and 404 dont mix!!
You need to clean the system from all traces of mineral oil.
New condensing unit is good idea.

I have done similar, the only issue is the residual mineral oil wants to be under 5%, as most of the oil is in the compressor you will be well on your way by changing the condensing unit. The compressor would benefit from an oil change once the system has run a few hours, so you may like to think about piping arrangements to make draining the oil easier.

If it is a chiller and not a freezer then you might like to consider R134a instead of R404A due to its lower gwp and its less likely to get banned or highly taxed like there is talk of doing with the high gwp refrigerants.

I am going ahead with a total refit. New blowers, pipework, cond unit, danfoss controller.

I am fitting a twin fan searle tec6 which weighs just under 20kg. I have been told I would be ok just to use self tappers to the roof. I think it would be better with 4x m12 drop rods to make sure it wont go anywhere. I have got an idea what to do but not sure what other parts I need for the rods??

Quote:

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Originally Posted by tonashp

I am going ahead with a total refit. New blowers, pipework, cond unit, danfoss controller.

I am fitting a twin fan searle tec6 which weighs just under 20kg. I have been told I would be ok just to use self tappers to the roof. I think it would be better with 4x m12 drop rods to make sure it wont go anywhere. I have got an idea what to do but not sure what other parts I need for the rods??

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20kg is nothing for the roof but too much to use self tappers.
All the wholesalers sell plastic rod and all the fittings needed
to use them. basically for such a small weight, all you would
need to do is put the holes through and then use the plastic
rod with the washers that you should get with it.

If you need to spread the weight of the evaps back to the wall
then unistrut cut to the correct size will do that, but at 20kg
I would just bolt straight through and use washers above.

If you have already chosen the refrigerant, so be it but for
future proofing the system I would consider other ones to 404a.

R404a will become a very expensive refrigerant in the future and
there are alternatives on the market that would replace it.

The EU are going to put a green tax onto refrigerants and it
will be liked to the GWP, 404a is quite high and will be hit
by any tax imposed on it.

See

http://www.acr-news.com/news/news.asp?id=3084

Rob

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Hi rob.

thanks for the reply. I have been to the wholesaler and purchased all the rods and fitting.

I do understand that theh want to move people towards the newer gases, ie r290, care. The same has been said about r134a that it will be the next to go. Very hard to guess who will face the chop first.

after all they are still in the process of phasing out r22 & I am still seeing loads of ac and fridges running happily on it.

Its sounds like you have it sorted, but i would just like to add that the supports need to take not just the dry weight of the evaporator but also its possible weight should a fault develop where it freezes up solid.
I generally estimate what it would weigh if i filled the case up with water, so a 20kg evaporator could weigh 50kg if frozen up which could be too much for a few self tappers, especially if they or the tin roof rusts a bit over time.

That is a very good point. I am sure that will spread the load evenly. The roof looks very good as that is where the condensing unit will soon live lol

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Many moons ago I got a call to attend a large cold store
after a report that the roof had fallen down.

When you here reports like that you sometimes wonder
if there was a bit of panicked exaggeration from the customer
and when on site the reported roof falling down was nothing more
than a fitting from the ceiling or a small section of a panel.

Not in this case, when I got to the site the reported roof falling
down was no exaggeration and it was well an truly collapsed.

The roof vapour barrier had gone and the roof had slowly been
absorbing moisture that was freezing and eventually the supports
could not take it any more and the roof dropped into the cold room.

There was even a fork truck underneath it and the driver had ran
out as he heard it coming down (he was very, very lucky).

Now this cold room was the size of a football pitch and was 12 maybe
15 metres high and the first half had collapsed down. The amazing thing
was the attached evaporators where still working and no refrigerant was
lost, which was amazing, considering the amount of damage it caused.

Rob

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I did purchase 4x 1metre m12 rods for a searle tec twin fan blower. I think I will use 6rods to support it, as discussed it's better to be safe than sorry.

I went a while ago do a display fridge that had "exploded" emergency call out, drop everything to go as that needed to know if it could be fixed or scrapped. Thinking I have never seen a commercial fridge explode, I imagine they will have the shop closed and case stored away. I arrived, case was outside in the yard, shop open as usual. Looked over put some gauges on to see, no pressure, pressure tested and found a braze on the drier had let go and let go of all the refrigerant, not quite the job I expected.

I went out to a co op in Essex one afternoon after a report of all their refrigeration going high temperature. On arrival I found all the pipework had been stolen! Cut off at the packs at the back of the store and flush to the wall. Oil and lagging everywhere!! All done in broad daylight, no-one saw a thing!?! I would love to have seen the guy cutting through the discharge! I wonder if the couple of hundred quid was worth all the freeze burn? Also went out to an office block in Birmingham whose heating wasn't working. Found a whole Daikin VRV condenser missing!! Amazing.

Just a Followup question. It's been running a few months now and a persistent problem is icing up. I moved the cond unit outside about a month due to heat from summer. Decided to make sure the defrost probe was in the top of the Evap away from the heater. Moved the room probe to the middle of the room in line with a dial thermometer. Went back 3days after the cond unit was moved outside and unit changed to pump down and it was iced up solid. Customer said it froze the meat so he changed it from 1.0 to 3.5degrees. I changed the defrost from every 6hrs to every 4hrs and from 20mins to 30mins with a termination temp of 12degrees

I have checked everything. Full sight glass, cuts out at 0bar on pump down. There is no gaps in the door seal. I have had the equipment checked that is sized up right but this problem persists.

Any ideas guys?

Have you any system running conditions ie
Suction pressure and Temperature
Temperature of the suction pipe next to the expansion valve bulb
Discharge Pressure and temperature
Liquid line temperature before the expansion valve
Kr Glenn

Along with Glen's questions:
Did you checked that defrosting operation is fully performed and all ice is melted at each defrost?
What is drainage time?
After defrost, at what evaporator temperature fan starts?
What is defrost type (hot gas, electrical)?
What is evaporator (not total) superheat?
What is evaporator TD?
What is evaporator approach?
What is evaporator air entering and leaving temperature?
Check evaporator air flow direction on all of fans and check (measure with air flowmeter) evaporator air flow volume against evaporator technical data.
What is evaporator make and model?
What is compressor make and model?
What is TXV make and model; orificeNo?
What goods and what are conditions of goods which entering coldroom? What is amount of that goods at 24 hour?
What i frequency of door openig and daily cummulative time of open door condition.
Where is evaporator postioned regarding door opening. Make some sketch or photo!

Are the fan blades on in the right direction? Usualy it is the little things that get you in the end!

drain blocked and coil touches water in drainpan?

Sounds like you bodged it! :eek:

I would go get all the readings as Glenn suggests.

Seems to be sorted now. Set point is 3deg with a 3deg diff. Upped the defrost duration to 45mins. No more icing up. I think when it was set for 20mins. It never allowed the heaters to warm up the coil before it was done (GEA Searle TEC) cheers for all the advice guys

Hi tonashp
Just a couple of points. When you set the pump down it should be set at a slightly positive pressure ie 0.3 Bar cut out, at 0 Bar during pump down you could potentialy suck air into the system if there is a leak in the systems low side. Also with a room temp of 3 degrees you should only need to defrost every 6 hours, with a 45 minute duration with a temperature termination as back up.
If you visit site again when the system is running measure the suction pressure and the temperature of the suction pipe where the TEV bulb is strapped, as I suspect you are running with a depressed suction condition which is causing heavy ice build up
Kr Glenn

Thanks Glenn.

I will check again. When it was firstdone the condensing unit was on the roof of the coldroom and was turned on and off by the controller . No pump down. Controller was originally set for defrost every 6 hr for 22 mins. When the condensing unit was moved. I changed it to pump down to try and stop the icing up. Also changed it to 30mins every 4 hrs. About 2 months later the solenoid valve failed and a new one was fitted and drier. At this point I changed Iit from 30 to 45 mins. I will try and tweak the LP.

Just had a call from the customer saying he is still getting sticky sausages he thinks it's too warm for too long. I changed the defrost last time I was there to 6hrs 45mins as suggested. He said the icing problem seems to have gone. The temp is set to 3deg with a 3deg diff. I will drop the temp to 2deg, but are still concerned about the icing up. I will try and get a temp of the bulb when I visit over the next few days.

Can you explain "depressed suction" as I have never heard the term before?

Quote:

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Originally Posted by tonashp

Just had a call from the customer saying he is still getting sticky sausages he thinks it's too warm for too long. I changed the defrost last time I was there to 6hrs 45mins as suggested. He said the icing problem seems to have gone. The temp is set to 3deg with a 3deg diff. I will drop the temp to 2deg, but are still concerned about the icing up. I will try and get a temp of the bulb when I visit over the next few days.

Can you explain "depressed suction" as I have never heard the term before?

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I think what Glenn is referring to is the pressure drop over the suction.

The longer the pipe and the more it bends the greater the pressure drop,
so at the compressor, you see a depressed suction.

If the pressure you read at the comp is lower than the actual evap pressure,
you get a false reading and different superheat settings.

On complex systems it is wise to fit a Schrader valve in the evap suction and
measure the pressure from there, with no pressure drop.

Regards

Rob

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Hi tonashph
When a system is designed you choose the Evaporator Temperature difference (TD) that you want the system to run at. The TD is the difference between the Room temperature and the Evaporating temperature. The TD you choose depends on the product your storing.
For a beer cellar you could had a TD of 10k as the product would not be harmeed as the product is sealed from the room condition in bottles. If you had a 10k temperature difference storing fresh meat, the meat would quickly start to shrink and dry out as the room humidity would be lowered due to the low evap temp.
If you went for a very low TD the meat would become slimy with the possibility of mould growth due to the very high humidity in the room.
So we tend to choose around the 5 to 6 K TD as this tends to give the best results for meat and fresh veg etc, with minimal product shrinkage.

So typically in your case with a room tempertaure of 3 Deg C you should be evaporating at minus 2 or 3 DegC. ie 5 K TD. If your room temperature is plus 3 Deg C and your evaporating temp is say minus 10 Deg C ie 12 K TD we then say we have a depressed suction, ie its evaporating temperature is much to low for the system.
This may be caused by an incorrect orifice in the expansion valve, a poorly adjusted expansion valve, having the TEV bulb in the wrong place on the suction line, under charged, etc etc.
The depressed suction will inc rease the icing up of the coil, give poor product quality ,giving increased energy usage due to longer running times.
If you can send me a running log of the system I will have a look to see if anything is wrong
1) Suction pressure
2) Suction Pipe temperature near the TEV bulb
3) Discharge Pressure
4) Liquid line temperature at the TEV inlet
5) Room Temperature

This is best done soon after a defrost has occurred at the system has stabilised. Glenn