Free cooling Systems

[T.M.Haja Sahib]

Hi guys,
We are installing free cooling systems in small Telephone exchange buildings with an intention to save energy.In order to verify whether there is any energy saving due to installation of free cooling system,we compare the energy consumed in a particular period after the installation of free cooling system with that of the corresponding period of the last year..In some cases,there are positive savings and in other cases there are negative savings. The building is provided with electromechanical disc type energy meter by power supply company.Such type of energy meters are inaccurate and the concerned power company did not calibrate them regularly.My question is whether the above procedure is valid or not and the positive and negative savings are really due to meter errors.Thanks.

 

[Jraef]

Other than what we call " creep" from being open circuited, rotating disk kWh meters are not known for needing calibration and at least here in the US, the accuracy class is never worse than 0.5%.

My first inclination, being that the term "free cooling" itself already sounds like a scam, is that your "positive savings" are the error and your "negative savings" are your real costs.

 

[T.M.Haja Sahib]

Other than what we call " creep" from being open circuited, rotating disk kWh meters are not known for needing calibration and at least here in the US, the accuracy class is never worse than 0.5%.

With passage of time, the electro-mechanical rotating disk kWh meter installed at site tends to slow down and do not record small loads.This would result in 'positive energy saving'.But how comes 'negative energy saving'?This may be highlighted.

 

[bob]

Hi guys,
We are installing free cooling systems in small Telephone exchange buildings with an intention to save energy.In order to verify whether there is any energy saving due to installation of free cooling system,we compare the energy consumed in a particular period after the installation of free cooling system with that of the corresponding period of the last year..In some cases,there are positive savings and in other cases there are negative savings. The building is provided with electromechanical disc type energy meter by power supply company.Such type of energy meters are inaccurate and the concerned power company did not calibrate them regularly.My question is whether the above procedure is valid or not and the positive and negative savings are really due to meter errors.Thanks.

1. I would like you to explain more about the "Free Colling System" and why you consider it free. Is this a comparison between the old
cooling system and the new cooling system?
2. As JR said, disk type meters used utilities are very accurate and require a test every 10 to 12 yrs. Most are found to be within tolerance
after the test.
3. Comparing the two periods of time for a test would be a way to check usage but you would need to verify that the weather and temperature were the same
or nearly the same. Can you say that the building had the same loads during both periods except for the A/C?
4. If you are concerned about the meter accuracy, why not have the utility test the meter and verify the accuracy?
5. I would have preferred comparing two consecutive months rather than two that are a year apart.

 

[iwire]

The accuracy of the meter is of little concern as you are looking for a change, not a reading.

 

[raberding]

free cooling

free cooling

perhaps it should be discussed with an HVAC professional. "free cooling" is a term used when outside air is used instead of mechanical cooling.

 

[bob]

perhaps it should be discussed with an HVAC professional. "free cooling" is a term used when outside air is used instead of mechanical cooling.

I doubt it.

 

[jim dungar]

... concerned power company did not calibrate them regularly.My question is whether the above procedure is valid or not and the positive and negative savings are really due to meter errors.Thanks.

In general I would expect a change in a specific meter reading to be in direct relation to a change in energy consumption, not in meter accuracy.

The power company has a very large financial and regulatory (legal) interest in having their meters accurately reflect the energy used.
Very few of their electro-mechanical meters are as inaccurate as customers are led to believe, by 'energy saving specialists'.

Yes, there are cases where individual meters have been under recording, but their percentage of the installed base is extremely low.

 

[hillbilly1]

I had an industrial customer that I had installed a new service for, their power bill had decreased even though they added more equipment. About eight months later the POCO sent them a bill for $40,000. The meter installer wrote in the wrong multipler!

 

[T.M.Haja Sahib]

The accuracy of the meter is of little concern as you are looking for a change, not a reading.

My dear iwire,you did not realise the assumption behind your statement:accuracy remains the same at the beginning and end of the change.That is the issue here.

 

[T.M.Haja Sahib]

Other than what we call " creep" from being open circuited, rotating disk kWh meters are not known for needing calibration and at least here in the US, the accuracy class is never worse than 0.5%.

My first inclination, being that the term "free cooling" itself already sounds like a scam, is that your "positive savings" are the error and your "negative savings" are your real costs.

Thanks JR for your clue about meter creep.I would try find whether there is a link between that and negative savings at sites.

 

[T.M.Haja Sahib]

1. I would like you to explain more about the "Free Colling System" and why you consider it free.

The high power air-conditioners are switched off and low power free cooling system is switched on when outside ambient temperature and humidity are low.This low total heat outside air is used for cooling,which is 'free'

2. As JR said, disk type meters used utilities are very accurate and require a test every 10 to 12 yrs. Most are found to be within tolerance after the test.

Yes.The disk type meters are very accurate in the beginning.But their accuracy deteriorate in the long run due to presence of mechanical components.

3. Comparing the two periods of time for a test would be a way to check usage but you would need to verify that the weather and temperature were the same or nearly the same.

Yes.You are correct.

4. If you are concerned about the meter accuracy, why not have the utility test the meter and verify the accuracy?

I wanted to have a brainstorming session with you all before taking a decision.

5. I would have preferred comparing two consecutive months rather than two that are a year apart.

Why?

 

[T.M.Haja Sahib]

I doubt it.

Why?

 

[USMC1302]

I don't think the accuracy of the meter would be as relevant in the overall picture as a comparison of heating and cooling degree day units. If I understand your situation correctly, you are running some type of refrigeration unit in these facilities, but have now also added the capability to use outside air exclusively if the situation permits? you need to determine how much run time the outside air was used as opposed to the refrigeration unit.

 

[iwire]

My dear iwire,you did not realise the assumption behind your statement:accuracy remains the same at the beginning and end of the change.That is the issue here.

Listen Haja,

The meters accuracy will change very little, if at all, over the course of a year.

This small change will not have much effect on your figures.

What makes your method worthless is the fact you are counting on the cooling demand to be the same this year as the last.

 

[iwire]

Yes.The disk type meters are very accurate in the beginning.But their accuracy deteriorate in the long run due to presence of mechanical components.

You keep saying that but you have shown no reference to prove it.

On the other hand many here with a lot of real world experience have told you that testing these meters has shown little inaccuracy.

 

[T.M.Haja Sahib]

What makes your method worthless is the fact you are counting on the cooling demand to be the same this year as the last.

Let the cooling demand remain the same.What are your other objections,if there are any?

 

[T.M.Haja Sahib]

You keep saying that but you have shown no reference to prove it.

.

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

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

 

[GeorgeB]

Let the cooling demand remain the same.

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.

 

[kwired]

Let the cooling demand remain the same.What are your other objections,if there are any?

But right there may be the problem, you have not mentioned if the cooling demand was the same for each period. Same meter may have a positive result one year and a negative result the next. Temperature and humidity for the compared time periods will make a difference. So will conditions that effect the temperature within the cooled space.