ambient temperature for outdoor units

[johno12345]

Hi,

Im trying to cool a small workshop that is brick built inside a warehouse that is about 50c.

We dont have the budget to splash out on new systems with long refrigerant runs so I wanted to buy a couple of second hand Mitsubishi Electric 12kW ceiling cassettes and mount the indoor unit on the roof of the workshop. The only problem is that the outdoor unit will be sat in the warehouse at 50c.

I know this will reduce the effacacy of the units but will it still work?

Thanks for any advice

[Tesla]

That's not a very cool idea - have you considered the other people who would work in the warehouse? The heat rejected from WS will multiply in warehouse area. Best bet is to reject the heat on the roof of the warehouse - it would not cost too much extra, over all you would likely save on the power from improved efficiency.

[johno12345]

the warehouse is always about 50C, its a steelworks I cant put them on the outside roof as it is too high, the only other walls are public footpaths

Without running very long refrigerant pipes, it wouldnt be possible to fit them outdoors

what does WS mean?

thanks for the advice

[moondawn]

think ws is meaning workshop

[sedgy]

hi johno, this in the uk is it? well the ambiant is cool enough 9 months a year there and its free apart from the fan + duckting, you could then add a fully contained unit if you feel you need mechanical cooling later ,

[johno12345]

sorry, im not being clear

i have a very big warehouse, always 50c inside due to the production processes. within this big warehouse is a small workshop which is stifling inside due to the process they use which causes high humidity.

It will need cooling all year round

and yes, sadly, im in the UK

[B G Scott]

It ain't much fun in those temperatures, many years ago (40+) I worked in a forge in Canada looking after the crane cab air conditioning kit.
Drivers would park the crane over the hot melt and go for a break and wonder when they came back why the a/c was not working.
We spent most of our shift just reseting HP controls.
The design of the kit today will not be up to what you are asking it to do.
Back then the condensing units were belt driven so the worst case scenario was a burnt out motor, easy change no refrigerant contamination etc.

Looks like you need to re think this one or budget for on going kit replacement.

[johno12345]

i think for the cost of the job, its worth a punt, and should get them working in a safer environment faster. hopefully, late this week/early next.

i know what you mean about parking cranes in daft places. they park ours under the lights and complain its gone dark!

thankfully, we have remote cranes and pendant cranes. id hate to see the risk assessment for a cab crane in these conditions.

[Brian_UK]

Make sure that condenser coil cleanliness is paramount on the maintenance aspect.

[mad fridgie]

A simple way to solve your problem is to but a mister infront of the air intake to the out door unit, this can be done with a very fine spray or a soaked mister pad. So you evap cool to the condenser. I think but I could be wrong that the maximum air on to these units is 43C

[sedgy]

hey johno, if its 50c inside the building , WHAT IS THE AVERAGE TEMP OUTSIDE? so why not use free cooling through duckting to get this?

[sedgy]

johno . build your workshop outside the main building, job done

[Thermatech]

If the Mitsubishi split systems are newer R410a inverter type then the max outdoor temp rating should be 46 deg C.
The problem that you will find is that at this extreem temp the outdoor unit will be moitoring data from the temperature sensors & will slow down the compressor to avoid excessive compressor discharge temperature & self distruction.
You may also find that the outdoor unit will not run all the time as it may keep stopping due to excessive compressor discharge temp & the system may stop regularly on a fault due to this problem.
The compressor life will be short due to this extreem operating condition & the cost of replacement will be more than the extended interconnecting pipe run for the alternative outside location for the outdoor units.
So you would find that the cooling capacity will be greatly reduced due to the extreem high air temp at the outdoor unit.

For this type of system you should be able to go for at least 80m pipe lenght this will also come with a performance reduction of up to 25% but at least the outdoor unit will be in more reasonable ambient & will be able to run flat out to provide at least 75% of the nominal cooling duty.

[johno12345]

Hi,

Thanks for the comments, the units will be well maintained and cleaned. The temperature isnt actually as high as i mentioned, it does get to 50 but only for short periods, the majority of the time its about 40.

The units are R22 units and will be running on R417. They are over sized for the area.

Sadly, i cant move the workshop.

The ironic thing is that I have 12 big evaporative cooling towers on site but thats another story.

I will give the long pipe runs some thought.

Thanks

[Makeit go Right]

The units are R22 units and will be running on R417.

Thermatech has given a good explaination of what could be expected with these systems, if trying to give off their heat to an already very warm workshop. You could also give a call to the technical department of the manufacturer and see if they can advise further.

Also talk to them about your plan to change over to R417a; you might be better keeping them on R22 than R417a.

(I wouldn't worry about making the workshop any warmer - sounds like it is a massive place and this would do nothing to the overall temperature.)

The longer pipe runs are the only way to make sense of this investment. A fair amount of money will be spent installing these two systems, and if they fall over after 3months, with spare parts harder to find (old R22 kit) you may have to replace them before very long. A poor investment.

The ironic thing is that I have 12 big evaporative cooling towers on site but thats another story

Well, there are Versatemp units which might be able to make use of that condense water to cool the workshop. You'd need to get a versatemp chap to visit site and see if it is viable/practical. Then compare the outlay with this split-type option (long pipe run).

[johno12345]

Ill have a look into using the cooling towers but dont think its viable due to the long periods of shutdown and the regular cleaning that we do on them

I would prefer to run them on R22 but as the refrigerant will have already been disposed of, i dont think we have much choice.

And, you are right, the additional heat loading of the outdoor units in the warehouse wont make a bit of difference. its that hot with all the roller doors open all year round

[Tesla]

Hi Johno
perhaps one option is to follow the above advice and go for a water cooled condenser, if not on those extra hot times use the water cooling atomiser on the condenser (this may give you best bang for your buck and keep the system within operating limits). That is if water usage is not a problem. On window rattlers the cool condensate water (from evap) is used to help cool the condenser.