3 min read

Chiller Efficiency: Cold to Hot 

As we learned in part 1, hot to cold temperature transfers involve the absorption of indoor heat, which is dumped outdoors. Because the chiller is working against the usual way of heat transfer (to produce cooling), its energy output is lower than the electrical input.  

This gives us a simple output to input ratio of less than 100%, which is used to describe efficiency. This is measured under different operating conditions, leading to specific metrics such as EER and SEER. 

However, for heat pumps that process – heat from low temperature ambient air, machines are using the heat energy from low temperatures to in turn produce more heating energy. Even air that is ‘cold’ by standards of human comfort has heat in it. Using heat to create heat naturally leads to higher input to output values than extracting heat to create cooling. For this reason, their heat output is higher than the heat equivalent of the wattage input. This creates a value greater than 100, which is misleading at first.  

Because losses always occur due to friction and the conversion of electrical energy to mechanical energy, it remains impossible for a cold to hot heat pump to have an efficiency of 100%. The best way to compare efficiencies of chillers in heating mode is to understand that at the end of the day, just as with cooling chillers, the greater their output to input ratio, the more efficient they are. In this case, the ratio will be described in decimals. For instance, a 1.5 ratio represents more efficiency than a 1.4 ratio.  

Heat Pump Efficiency is not Black and White 

Rather than the EER and SEER metrics used for hot to cold temperature transfers, IPLV, NPLV and SCOP are used as efficiency metrics for cold to hot temperature transfers. 

While heat can be extracted from low temperature air, the colder the air is, the more difficult it is for heat pumps to do so. This is the primary attribute that heat pumps must possess in order to score highly on heating tests – the ability to extract heat efficiently. 

IPLV 

Comparable to the EER and SEER metrics used for hot to cold transfer, IPLV stands for ‘Integrated Part Load Value.’ It is a weighted average of the energy efficiency ratio (EER) calculated at each stage of the unit’s unloading operation range

In most use cases, where machinery is not operating close to its full load value, a lower IPLV is desirable. 

NPLV

NPLV (Non Standard Part Load Value) is similar to IPLV, but is based on a chiller loop temperature of 55°F, rather than the 44°F used for IPLV tests. 

COP/SCOP 

COP and SCOP are based on both capability and efficiency with a chiller/heat pump in heating mode. 

COP is calculated through dividing net capacity by power input, as well as gross cooling capacity minus supply fan heat, divided by supply fan + compressor(s) + condenser fan(s). SCOP, meanwhile, is calculated with the same metric, taken under different operating conditions, with the weighted average across all tested conditions displayed as the final result. 

The Most Efficient Heat Pump According to COP

Clivet’s WiSAN-YEE1 offers the highest seasonal efficiency in heating, with A++ class efficiency. 

With a scroll inverter compressor, wide operating envelope, s and R32 refrigerant, the WiSAN-YEE1 Large Evo is more than just efficient. It’s eco-friendly with the low GWP of just 675, with low noise operation and extended operating limits for flexibility and reliability. 

With SCOP of up to 4.22 and SEER of up to 4.51, it offers incredible performance and low-cost operation no matter the season. 

Now That You Know 

Now that you understand the variety of standards to which chillers and heat pumps have their efficiency rated, you can scan the market with an educated eye. Remember that EER and SEER are used for Hot to Cold performance, while COP, IPLV and NPLV are used for Cold to Hot performance. 
Keep this in mind when comparing quotes and specifications! If you’re after a high efficiency chiller for a replacement or new project, Masterflow is the place to go. We have a great relationship with Clivet, who are an innovative leader in the chiller industry with elite efficiency, standout features and excellent reliability.