CR4® - The Engineer's Place for News and Discussion®


Previous in Forum: Excess Steam Quench / Seal Leaking From Asphalt Pumps   Next in Forum: Back Gouging on Single "V" Butt Joint
Close
Close
Close
21 comments
Participant

Join Date: Jul 2017
Posts: 3

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

07/25/2017 9:47 AM

Dear All,

This is the first time I am posting a query on CR4, I am sure a similar query would have been raised on some different forum.

My queries are below:

1. Why condensing pressure drops when ambient temperature reduces? Can't we crank-up the compressor to maintain high discharge pressure?

2. What are the operational problems faced by an air conditioning equipment during low ambient condition specially in sub zero conditions?

3. What are the ways to overcome the challenger, I am sure in colder regions of US or Europe air conditioning (cooling) will be required to cool data centers or offices.

Regards,

Rohit Goel

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26716
Good Answers: 701
#1

Re: Condenser Head Pressure W.R.T. low ambient temperature

07/25/2017 9:57 AM

A1) Because the liquid/vapour transition temperature of any fluid that is below its critical point is dependent upon pressure, and vice-versa.

A2) In sub-zero ambient, the problem reduces to simple ventilation, as the "coolth" is being supplied by the environment.

A3) Opening the window is often a solution. Beyond 55deg latitude, no-one needs air conditioning.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 2)
Power-User

Join Date: Nov 2008
Location: Seoul, Republic of Korea
Posts: 288
Good Answers: 26
#16
In reply to #1

Re: Condenser Head Pressure W.R.T. low ambient temperature

07/26/2017 8:00 PM

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.

__________________
Free advice guaranteed or your money back
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26716
Good Answers: 701
#21
In reply to #16

Re: Condenser Head Pressure W.R.T. low ambient temperature

08/03/2017 3:53 AM

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

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#2

Re: Condenser Head Pressure W.R.T. low ambient temperature

07/25/2017 11:06 AM

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?

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26716
Good Answers: 701
#3
In reply to #2

Re: Condenser Head Pressure W.R.T. low ambient temperature

07/25/2017 11:46 AM

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#4
In reply to #3

Re: Condenser Head Pressure W.R.T. low ambient temperature

07/25/2017 12:09 PM

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

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26716
Good Answers: 701
#8
In reply to #4

Re: Condenser Head Pressure W.R.T. low ambient temperature

07/26/2017 3:46 AM

No offence taken. It was just a hilarious question!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 19288
Good Answers: 1129
#5

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

07/25/2017 2:19 PM

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....

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Participant

Join Date: Jul 2017
Posts: 3
#9
In reply to #5

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

07/26/2017 4:09 AM

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.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26716
Good Answers: 701
#10
In reply to #9

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

07/26/2017 6:35 AM

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)?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Participant

Join Date: Jul 2017
Posts: 3
#12
In reply to #10

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

07/26/2017 8:02 AM

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.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26716
Good Answers: 701
#13
In reply to #12

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

07/26/2017 8:06 AM

Why?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Associate

Join Date: Jan 2009
Posts: 30
Good Answers: 1
#15
In reply to #12

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

07/26/2017 6:35 PM

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

Register to Reply
Commentator

Join Date: Dec 2010
Posts: 79
Good Answers: 3
#11
In reply to #9

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

07/26/2017 7:48 AM

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.

Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#14
In reply to #9

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

07/26/2017 9:27 AM

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...

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#18
In reply to #9

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

07/27/2017 9:01 AM

Change working fluids. Enough said.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19990
Good Answers: 750
#6

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

07/25/2017 3:23 PM

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

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
2
Commentator

Join Date: Dec 2010
Posts: 79
Good Answers: 3
#7

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

07/26/2017 2:37 AM

Refrigeration operates within certain parameters and when the outside air temperatures drop the condenser fan must run slower to prevent the low head pressures you are seeing. This is called a low ambient kit and to maintain head pressure some styles simply cycle the condenser (outside) fan on and off accordingly. Also when ambient is below 55 degrees F for example an economizer would be a better option than mechanical cooling as outside air can be simply drawn in for cooling.

Register to Reply Good Answer (Score 2)
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19990
Good Answers: 750
#17
In reply to #7

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

07/26/2017 8:13 PM

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

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Associate

Join Date: Apr 2016
Posts: 34
Good Answers: 3
#19

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

07/28/2017 6:54 PM

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.

__________________
Real men don't set for stun!
Register to Reply
Commentator

Join Date: Dec 2010
Posts: 79
Good Answers: 3
#20

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

07/28/2017 7:07 PM

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.

Register to Reply Score 1 for Good Answer
Register to Reply 21 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

huntman10 (1); James Stewart (4); Mr Fixit (1); normnet (3); PWSlack (6); rohitgoel1210 (2); simonsd (1); SolarEagle (1); Tornado (2)

Previous in Forum: Excess Steam Quench / Seal Leaking From Asphalt Pumps   Next in Forum: Back Gouging on Single "V" Butt Joint

Advertisement