Depending upon the size of the complex and application, a variety of options are available for air-conditioning.  The choices of systems available are summarized in Table 1:

Different standards are used to evaluate various options.  The most commonly used are AHRI (Air-Conditioning, Heating & Refrigeration Institute, originally ARI) and the JIS (Japanese standards). IS or the Indian Standards are limited to small systems such as splits and window units; hence, AHRI is generally used, which is a US standard. The most relevant standards are:

1. AHRI 210-240 Performance Rating of Unitary Air-Conditioning and Air Source Heat Pump Equipment   
2. AHRI 340-360 Performance Rating of Commercial and Industrial Unitary Air-Conditioning and Heat Pump Equipment
3. AHRI 550-590 Performance Rating of Water Chilling Packages Using Vapor Compression Cycle

A standard is used to establish test and rating requirements which form the basis for manufacturers to publish ratings.  To give you an idea, we are reproducing some of the test conditions for measuring the capacity and power consumption of the unit.  See Table 2.

Manufacturers provide the performance rating charts showing capacity and power consumption at various operating conditions, which can be used by consumers while selecting the system.  Depending upon the peak load conditions of the particular city, appliance of required capacity is selected.  And the appliance having maximum efficiency – EER, i.e. Energy Efficiency Ratio (EER = total cooling effect ÷ power consumed) obviously becomes the first choice.  However, the EER value, for which the appliance is selected, is the value for that particular selected operating condition; it may not give the true reflection of energy efficiency for full year of operation.  That’s because the indoor and outdoor conditions across the entire year of operation keep varying and do not remain the same.  If we plot the hourly temperatures through the year in a particular city and calculate the hours the system runs on peak demand, it would only be 4% to 6% of the total operating hours in a year.  This means that the system is operating at part load conditions most of the time.  Thus, the EER at part load is very important.    It is known that many systems  offer high EER at maximum capacity but suffer considerable degradation at part loads.

This has lead to the concept of IPLV. For larger systems, we use the Integrated Part Load Value (IPLV) as an important measure of performance throughout the year.  As per this standard, EER at 4 capacity points are measured – 25%, 50%, 75% of full load and the full load point.  The ambient is kept at 27°C and the indoor is also kept at 27°C.  Once the EER at the 4 points have been measured, a weighted average formula is applied to calculate and get the IPLV. A sample calculation of IPLV of a Digital Scroll VRF system is shown in Table 3.