Free cooling Systems

[raberding]

free cooling

free cooling

then perhaps "free cooling" is not the correct term

http://en.wikipedia.org/wiki/Free_cooling

 

[USMC1302]

Even if the cooling demand was the "same" as you say, the run time of your free cooling vs DX system could very well be different.

 

[hurk27]

So why not just compare the energy usage of one system against the other system, this takes out all the variables and gives you a direct comparison?

 

[USMC1302]

Exactly...if the units are separate. The point being, the electric meter readings aren't enough info to make a fair comparison.

 

[dpeter]

This year energy verses last year energy will be a waste of time and add confusing and conflicting data. As mentioned before, the cooling and heating degree days will make a diference as well as load and when the load and outside temperature and humidity would allow for free cooling. If you were not, and now are, able to use outside air instead of mechanical cooling, then you are most certainly saving money. To quantify your savings all you need do is to figure the difference in energy used by a compressor and fan to that used by only a fan. The result is your savings and you only save it when you're using FREE cooling.

 

[iwire]

See clause-3 in the link below,for example.

http://www.analog.com/static/imported-files/tech_articles/5779410760_year_life.pdf

Worthless link.

• Your link is from someone trying to sell electronic meters.
• Your link has no studies or statistics about meter inaccuracy
• Your link only mentions that mechanical meters can have have issues.

Forget the meter, your basic methodology is so flawed the meter will not mater.

 

[Jraef]

then perhaps "free cooling" is not the correct term

http://en.wikipedia.org/wiki/Free_cooling

Well, I for one learned something new today. Time to go home.

 

[T.M.Haja Sahib]

Forget the meter, your basic methodology is so flawed the meter will not mater.

Do you have any other 'sound' methodology in your critical mind? If yes,speak out immediately.

 

[T.M.Haja Sahib]

We had an expression in my youth relating to theoretical assumptions and engineers ... "Assume a spherical cow with equal milk distribution".

Only with a documented "degree day" table or graph based on desired conditioned space temperature (and humidity if applicable) would I "Let the cooling demand remain the same." be a valid way to make comparisons.

May I assume that you would be less critical,if you assume yourself in a brainstorming session and ideas such as "Assume a spherical cow with equal milk distribution","Let the cooling demand remain the same." etc.,arise in such a session?

 

[T.M.Haja Sahib]

This year energy verses last year energy will be a waste of time and add confusing and conflicting data. As mentioned before, the cooling and heating degree days will make a diference as well as load and when the load and outside temperature and humidity would allow for free cooling. If you were not, and now are, able to use outside air instead of mechanical cooling, then you are most certainly saving money. To quantify your savings all you need do is to figure the difference in energy used by a compressor and fan to that used by only a fan. The result is your savings and you only save it when you're using FREE cooling.

The operation of the air-conditioning compressor is also influenced by cooling degree days and load and so the difficulties encountered with this year energy verses last year energy may not be overcome by comparing energy consumed by compressor alone.I think it is not THAT WAY to quantify savings in free cooling.

 

[T.M.Haja Sahib]

So why not just compare the energy usage of one system against the other system, this takes out all the variables and gives you a direct comparison?

This method is not clear to me.Will you elaborate further with numerical examples,if possible?and how to calculate savings in individual systems?

 

[kwired]

The operation of the air-conditioning compressor is also influenced by cooling degree days and load and so the difficulties encountered with this year energy verses last year energy may not be overcome by comparing energy consumed by compressor alone.I think it is not THAT WAY to quantify savings in free cooling.

This method is not clear to me.Will you elaborate further with numerical examples,if possible?and how to calculate savings in individual systems?

Maybe you have not made it clear to the rest of us just exactly what is the load you are measuring.

If you are trying to maintain a specific temperature, the amount of energy needed to cool the space will depend on how much heat is internally gained plus how much heat is gained from outside. The internal gains possibly are more consistant and can be predicted more accurately. The outside gain depends on the weather. You can't just look at the high temp and low temp for each day, you need a good idea of what temperature was like throughout the day.

This "free cooling" system you are describing is intended to take advantage of cool external conditions when they exist. Not exactly free to operate but the heat source/sink is essentially free. If the cool conditions do not exist then you run your normal system just as you always have in the past.

How can you even suggest "let the cooling demand remain the same", when the cooling demand is determined in part by how much external heat gain there is, and you have not proven that it is the same?

If outside air is not cool enough you may actually be adding heat instead of removing it making the main system work even more thus the increase in energy usage in the cases where you see negative savings. If you are bringing outside air directly inside you could be increasing humidity which will retain internal heat easier than drier air.

This may be a little more of a HVAC topic than an electrical topic, have you tried any HVAC forums with your question?

 

[petersonra]

Maybe not an issue in India, but a fair number of companies here in the US have found that trying to use cool outside air has it's own issue. Often the humdity is low enough that you either need to use an air-air heat exchanger or add in a humidifier.

 

[T.M.Haja Sahib]

Maybe you have not made it clear to the rest of us just exactly what is the load you are measuring.

I mentioned in the OP free cooling systems were installed in telephone exchanges.

How can you even suggest "let the cooling demand remain the same", when the cooling demand is determined in part by how much external heat gain there is, and you have not proven that it is the same?

I already suggested it is an idea of brainstorming.

This may be a little more of a HVAC topic than an electrical topic, have you tried any HVAC forums with your question?

Do you believe electrical aspects of the problem are already thoroughly discussed or not?

 

[T.M.Haja Sahib]

Maybe not an issue in India, but a fair number of companies here in the US have found that trying to use cool outside air has it's own issue. Often the humdity is low enough that you either need to use an air-air heat exchanger or add in a humidifier.

Here in small almost unmanned telephone exchanges,cooling is for equipments and not for people,So cool and low humidity ambient air is admitted into the exchange by using sensors for ambient temperature and humidity.

 

[dpeter]

The operation of the air-conditioning compressor is also influenced by cooling degree days and load and so the difficulties encountered with this year energy verses last year energy may not be overcome by comparing energy consumed by compressor alone.I think it is not THAT WAY to quantify savings in free cooling.

This is exactly my point! Energy used this year verses last year is affected by all things previously mentioned and is therefore pretty useless for the purpose you are trying to use it for.
To be clear, I am NOT suggesting comparing anything this year against anything last year. Determine the energy used by the HVAC system while not using FREE COOLING and the energy used when free cooling is utilized. The difference will be your savings assuming there is one.

 

[petersonra]

Here in small almost unmanned telephone exchanges,cooling is for equipments and not for people,So cool and low humidity ambient air is admitted into the exchange by using sensors for ambient temperature and humidity.

The problem being that equipment that is static sensitive does not like low humidity. Somehow one has to be able to control the humidity as well as the temperature and in the US a lot of times cold air is quite dry which makes it not real suitable for direct exchange.

Admitting cold air into a hot humid environment can also result in condensation, which is not ideal either.

 

[USMC1302]

If you want to compare energy cost from one year to the next, find your net cooling degree days. Divide that into your energy consumption, so your result is energy/cooling degree day. If the ratio decreases, it would seem logical that your economizer cycle was likely contributing to your savings. This would be a rough comparison.

 

[defears]

First find out how many days a year on average that system could be useful in your area.

http://weathersource.com/past-weather/official-weather?gclid=CJKfqPq1m6wCFYuC5QodWxIs2g

Scroll down to custom settings for net cooling degree days. I'm sure there many more sites to find out that type of information. Who knows, it might not be worth doing if you only get a month or 2 a year to use it.

 

[hurk27]

Sitting here reading and it just hit me on how this colling works, in my little converted front bedroom that I made into my office, my computer uses a lot of energy, it has a 1200 watt power.supply and the cooling fans on it produce allot of heat, this room will run about 78?F to 85?F even in the winter time with the only vent turned off, well I have to do some free cooling since it is now cooler outside I can just open the window a little.

Now I can see where this system could be put to use in a telephone exchange or computer rooms/data centers where the operating equipment drives the temperature too high and it needs to be brought back down, this nothing more then opening the window, but through a heat exchanger to keep the environments isolated, I could see where this could save energy usage at certain times of the year, this has been used in large high rises and office buildings where the inside areas in the core of the building get too hot even while the exterior areas are running the heat, so why not just transfer the heat from the core areas to the exterior areas and save even more?

I know one thing is this type of system would be very complicated and would take a very specially trained person who understood the operation to keep it working but it would be feasible.