COP is a ratio of output input power. We provide simple COP metering method by linking up all meters via a 2-wire RS485 cable:
Each of our Data Appliance is capable to connect over 30 Modbus devices. It means you may use it to monitor COP of one single chiller, or a group of chillers. All you need to do is just to add extra sets of power meter and BTU meter. This kind of configurations apply the same to cooling towers and hot water boilers. If your plant is not powered by electricity but other energy sources like fuel gas, you can simply replace the above power meter with fuel gas meter with a Modbus output. Likewise if you are metering steam boilers you will replace the water flow meter to steam flow meter with a Modbus output.
COP is a simple ratio yielding from two parameters:
- Cooling or heating capacity of a plant
- Energy input, often electrical, to a plant to facilitate the above thermal change
In practical terms, it means we need two meters to get the nubmers
- Thermal Energy Meter: usually a fluid flow meter with two temperature sensors; also known as BTU Meter simply called Energy Meter.
- Power Meter: can be as simple as an electrical kWh meter, but nowadays it often comes with other quality measurements such as power factors and harmonics, along side with the basic power voltage and current measures; it is also known as Power Analyser
What is COP?
Coefficient of Performance (COP) is a ratio of work or useful output to the amount of work or energy input, used generally as a measure of the energy-efficiency of air conditioners, space heaters and other cooling and heating devices.
COP is generally used as a key performance index of heat pump. It means chiller or cooling tower or boiler in plain English. For the sake of easy discussion we often shorten the formula to become:
Higher COPs equate to lower operating costs. The COP usually exceed 1, because it is a ratio of output:loss. Measurement of COP is straight forward in engineering point of view, but becomes tricky when doing it contractually. It is because power output is generally contracted to HVAC contractor, while power input is a matter of Electrical contractor. As a result COP figure is available only in buildings/plant with a BMS or SCADA system install to consolidate measurements from the two different trades.
COP for Cooling Towers
Evaporative cooling towers are often running on open-loop water circuit, in which portion of the water is lost to ambient. The make-up water supply may not catch up accurately for a constant mass flow rate. Still the principle of COP applies the same on them, with the following elaborated equation:
= Cooling Capacity = Heat Rejection Capacity
= Fan Electrical Power
= Electrical power for the pump in Circuit 1 – often refers to chilled water circuit pumps
= Electrical power for the pump in Circuit 2 - often refers to condenser water circuit pumps
= Electrical power for the spray water pump
Cooling tower heat exchange efficiency is at times qualified by other methods. You may like to review this paper by Bengt Bergsten. The paper has sections discussing features of the Cooling Tower Model, CTM, the Merkel model, the CTI Toolkit, and the effectiveness – NTU method. A coefficient of performance, COP, is defined for a cooling tower or air-cooled heat exchanger.The paper has sections discussing features of the Cooling Tower Model, CTM, the Merkel model, the CTI Toolkit, and the effectiveness – NTU method. A coefficient of performance, COP, is defined for a cooling tower or air-cooled heat exchanger.
We have packaged solutions with the following meters:
- Thermal Energy Meter: Sitelab or Zenner (both are transit-time ultrasonic flow meters; both in-line or clamp-on type sensors are available)
- Power Meter: Janitza UMG 96RM or Schneider PM1200