Condenser Head Pressure W.R.T. Low Ambient Temperature

I had to go look at at a map and was shocked just how little occupied land is beyond the 55 parallels!

In the south its really just Antarctica and as mentioned below cooling equipment there is a matter of getting a big enough fan to blow the cold dry air over whatever is too hot.

In the north you are beyond any major cities in Canada and all of China, Kazakh, Japan and Korea. So the only band that might argue would be the 55-60 degree band of cities - Moscow, St Petersburg, Helsinki, Oslo, Stockholm. The problem in these cities is the period for which AC is needed maybe 2 months and whether that justifies installation.

Exactly. To achieve cooling one needs ventilation. Air conditioning is about comfort.

Do you have an ice cave where you are storing fish in Siberia? What is the operating environment, precisely, and why are you running in sub-zero conditions?

OK, my bad. Meant to reply to OP, not dopey.

No offence taken. It was just a hilarious question!

Mostly we use chilled water systems...generally with fresh air intake, that is adjustable...

http://www.greenseal.org/Portals/0/Documents/IG/PHA%20Manuals/Chapter2_Northern_Green_Building_OM_Manual_PHA.pdf

...there are also variable refrigerant flow systems....

http://www.seventhwave.org/cold-climate-vrf

...and heat pumps....

Thanks for your response, however my question was not related to heat pump or heating required during winters. My project, which is an upstream oil project and it is located in a cold climate (-36°C) and we need to cool (compressive cooling) electrical & control room during winters too. However, finalized vendor has stated that his equipment can't cool below -20 °C because of low condenser head.

I need to understand reason behind low head and what other vendors do to overcome the above challenge.

If the ambient is <...-36°C...> then ventilation is needed, not cooling. There is already a source of "coolth" immediately available!

Perhaps that is why the vendor declined to supply (rhetorical question - NNTR)?

Hi PWSlack, your responses are not helping. Flow rate of ambient air is fixed and I need compressive cooling in addition to ventilation (free cooling).

Thanks.

Why?

Your getting the best answers you can get with the limited information you have provided.

By compressive cooling I think your referring to mechanical cooling which has it's limits at quite higher temperatures you describe.

The two main issues w/ mechanical cooling @ the temps you describe is

A) The basic phase change behavior of the refrigerants used in mechanical cooling @ your desired temp range...

B) Considered by some the more important factor; the control of oil flow @ such low temps.The oil will migrate with the 'freon' & away from the compressor without sufficient heat (molecular energy).

You need equipment designed for such low temps.

The rest of the homework is yours.

J

What is the units normal head pressure? This can be maintained by use of a head pressure control which controls (slows) the condenser fan speed. Also referred to as a low ambient kit.

In other words all other conditions being equal if only the outside air temperature is changed then only the outside fan speed will require adjustment.

How cold do you need the freaking instruments and controls to be for proper functionality? This is so ridiculous - open a freakin' window.

I ask the same question as PWSlack in this case, WHY?

This whole scenario seems out of the norm...

Change working fluids. Enough said.

One way to do this is to use regulating valves that cause the condenser to fill partly with liquid refrigerant.

That works only to a point; in really cold ambients, even with all fan(s) idle, the condenser can still be "too large".

To make this a little clearer to understand, this type of 'refrigeration' cycle requires a change of state in the fluid, in order to force or 'pump' heat.

As the refrigerant is discharged from the compressor (it is at high pressure and heated by the compression cycle) and passes through the condenser, heat is rejected to the air (in your case, the outside air) and the lowered heat and increased pressure has made it a liquid. As the refrigerant liquid passes through the heat exchange coils in the evaporator, the evaporation of the refrigerant fluid absorbs excess heat energy from the incoming air, which is cooled by the transfer of heat (the side that cools your equipment).

If the heat rejection to the outside air (because the outside air is so cold) is greater than the design parameters, the refrigerant coming into the compressor will be too dense and difficult to compress. The solution, if you have to use your refrigerant cycle to cool your equipment, would be to add heat to the air on the condenser (perhaps, venting some of your waste heat from the processors to the evaporator) or perhaps waste heat from some other part of your facility. As James has pointed out, it might be possible (but probably would void every warranty on any part of the system) to find a fluid with different characteristics for cold weather operations (we won't even think about the stratospheric ozone implications of fiddling with that aspect).

It makes much more sense to blend outside air (unless, perhaps you have an air quality problem there) to achieve cooling needs, rather than trying to defeat thermodynamics of your refrigerant system. Save the power demand for warmer months. The logic for that type of system would be similar to that for a "heat pump" central heat system, that switches from heat pump to gas or resistance heat.

Is the climate almost always below 13/15 degrees C? If so 2 simple fan coils one in and one out connected with glycol-ed circulation piping and a pump may be sufficient. Requires only minimal wall space for piping and wires.