Heat Transfer Efficiency 4

[AKHou]

There's some debate in this camp regarding the gained (or lossed) efficiency with improving the heat transfer of a constant air volume air handler by cleaning the coil.

Assume a 20-story building with air handlers on every floor and a central plant chiller cooling a cold water loop.

One party claims the central plant chillers would see more load (from better heat transfer) and use more energy. I see it opposite - in that the chiller, over time, would use less energy because of the better heat transfer.

Any opinions on this would be appreciated.

 

[BronYrAur]

My thought is that your load is your load. If your coils are dirty and you are getting less heat transfer, then your chilled water valves are staying open wider and/or longer to deliver the required cooling. Your pump is also working harder. You didn't mention whether you have 2-way or 3-way valves. If you have 2-ways and your pump is on a VFD, you should see energy savings from clean coils, because your water flow will be less.

At the same time your air handler fans are probably drawing more current trying to push air through dirty coils. Cleaning the coils should save a little fan energy.

The chiller probably won't see much change because like I said your load is your load. I think the real savings is in fan and pump energy. The only way I see the chiller energy going up is if you are not meeting the load now and by cleaning the coils you will. In that case, you are actually transfering more heat.

This is just my "common sense thinking". I would be interested to see if anyone has conducted a study or has actual data on this.

 

[imok2]

There should be no debate on greater efficiency when one thinks in terms of COP (coefficient of performance)which is a term used to indicate the efficiency of refrigeration equipment. The higher the COP, the more efficient the equipment is. Effective cooling depends on the temperature as well as the moisture content of air.
COP = Effective cooling out/Work in.
I like to think about it in terms of PID in controls, you know, approaching the set point in the shortest possible time... therefor less energy use.

 

[insult2injury]

Definitely would save energy...if heat transfer rates are increased, then less chilled water is required to be produced and the chiller can operate at a lower setpoint and most likely more efficiently

 

[Lance7]

We demonstrate this all the time at work in all our tall buildings. Simply by shutting all the Air-handlers down watching the chill-water fall to its presetting at the chiller and the chiller goes idle to its lowest amps.

If you cannot transfer heat then you have no load. As said "your load is your load". You have nothing working harder, valves are valves and don't have a working load. Pumps don't work any harder in the loss of a heat load transfer. They maintain as they do any other day with a load.(unless you have a building with a pump driven frequency drive)