A/C Powermizer

[rhpe]

I have run across a device that claims to lower a/c cost by reducing the run time of the compressor so the air conditioner reaches max cooling temp with minimum energy usage. It does so by sensing the temp of the air off the evap coils and then turning off the compressor when certain conditions are met. The literature claims that compressors run most efficiently when fully loaded so upon start up the density of the gas is at its highest. The theory is to cool mostly in this condition. Has anyone done any analysis on these types of products. Thanks for any help.

 

[absrbrtek]

I havent done any analysis but it sounds like youll be short cycling the compressor before your stat meets setpoint. Your also most likely going to have a moisture removal problem. Ive seen this setup in action, only thing it does is create customer complaints.

 

[imok2]

I agree with absrbrtek on the probability of moisture problems. No one can say with certainty that these kinds of controls will work with a particular application. In most instances you just have to try it to really know.

 

[sterl]

For most compressors, operating at high proportion of peak gives best COP.

At the same time, most processes or interior space conditions won't permit the variances associated with flywheeling in a fashion like this...And they don't represent a large enough thermal inertia to avoid the short cycling indicated if try to maintain a narrow band of space conditions...

The systems that do tolerate this style of control have large thermal capacitances....Effectively they are inherent large flywheels.

The brine system in an ice rink contains some 8000 gallons of thermofluid and the chiller will operate in this fashion...

Similarly with some large vats where such materials as orange juice or liquid yeast are stored.

For anything like AC duty, you will end up with a pretty large sump or a pretty large silo and the losses to ambient and the control for Frost Conditions might make it all very clumsy.

 

[rhpe]

Thanks for the information.

 

[ClydeMule]

Yes, if you run one compressor for 2 hours, it will draw less power than one that runs for 3 hours.

Sounds like the same exact thing a normal tstat does, sensors is just in a different place.

Sounds like this thing is made my Articmaster.

Clyde

 

[ozmosis]

I suggest you look under the "Electric Motors and Motor Controls" forum as there are more threads on this subject than you can shake a stick at. The bottom line is: be careful and don't forget the basic laws of physics!

 

[buzzp]

I can say, in general, a motor operating a full load is more efficient than one operating at reduced load. However, when the motor is started and stopped frequently, this acts to reduce the life. So you could have a more efficient motor that will not last as long. There are several variables that must be accounted for before a savings can be realized. I would think each and every case would have to be treated seperately to determine if a savings can be had. But knowing salesman for OEM's I am sure they just tell you that all installations will save $ not just 30% of them using their product. Just some food for thought.

One other note just FYI: the same exact motor running for 3 hours vs. 2 hours may use less power than the one running for 2 hours if it is more closely matched with the load. Of course, the larger the motor then the more significant the savings. Granted, the frequency of this happening is probably not very often but is entirely possible. Also, it would depend on if your getting billed for only watts or if VAR's are also being billed (pf penalties and the like).

 

[rjhpe]

Yes, I understand the kva versus kw concept. Motors consume the same amount of reactive power at idle as they do at full loads--thus the concept of reactive power correction devices along the idea of reducing the reactive I2R losses. I think the manufacturer is claiming not a more efficient motor but a better COP by the operating the pump at a higer volumetric efficiency which the claim is under full load.

I'll think about this and get back with everyone if I come up with anything.

 

[nandiropa]

visit

http://www.acpowermizer.com

 

[friartuck]

I have come across control systems like this. A client of ours employed a 'energy consultant' who installed a timer which switched off plant almost randomly claiming that you wouldn't notice if an AC unit was off for 5 mins every 25 etc. The result was that all sorts of important machinery got switched on and off whether you wanted it to or not. The system was soon abandoned, though the theory is logical (though not necessarily workable)

Switching compressor motors etc like this is not advisable. Try inverter drives or more refined control mechanisms rather than simply switching on/off



Friar Tuck of Sherwood

 

[MintJulep]

Increasing the efficiency of one component does not necessarily increase the efficiency of the system.

Seeking increases in energy efficiency alone, while ignoring the necessary and intended function of the system may result in a system that fails to perform its necessary and intended function.

Thus far, the laws of thermodynamics have proved to be inviolable.