What Is a Good COP for an Air to Water Heat Pump?

The coefficient of performance, COP, is the ratio of heat or cold produced by a heat pump to the specific energy input. The ideal cop for heat pump systems starts from 2.0. That's for the air source heat pumps, while geothermal starts at 3.1. Still, the cop of a heat pump can be above 4.0. In the guide below, we will discuss the ideal COP of different heat pump units and the practical meaning of COP. 

What's the ideal COP for air to a water heat pump? 

If you are using a closed-loop heater pump, good COP will fall between 3.5 to 4.2. The maximum COP, on the other hand, should be 4.7+.

With an open loop, the idea COP lies between 4.0-4.5 while the maximum value is 5.0+. lastly, the direct exchange heater pump has a good COP of 4.1 and a maximum 0f 5.0+

COP should not be mistaken for an efficiency rating of air to water heater pumps. Air to water heat pumps has a SEER/ cooling rating of 13 in the northern US and 14 in the southern. They have a minimum HSPF/ heating rating of 8.5. 

Further, geothermal heat pumps are classified in terms of loops and water-to-air vs. water-to-water. You can also see their efficiencies here on Energy.gov page. Also, the most efficient numbers always take a +sign since efficiency improves yearly. 

Understanding Coefficient of Performance

As said earlier, the Coefficient of Performance is a performance rating. It shows how air to water heater pump transfers heat or cold versus the electrical energy used in effect. Remember, air to water heat pumps transfer heat from low-temperature zones to high-temperature regions. 

It’s against thermodynamics laws. Heat should flow from hot regions to cold regions. In this regard, the "uphill" heat transfer against heat laws requires work. COP, therefore, shows how effectively an air to water heat pump does this work. It states the power quantity needed by the unit to move a fixed measure of heat at a fixed temperature.

Should you be looking for how much heat the HP transfers when powered with a specific energy quantity, the COP is what you are looking for. For instance, air to the water heat pump with a COP of 2.5 will move 2.5 times more heat energy than eth energy it uses. 

So how do you determine the COP of your air to a water heat pump? 

Simply put, you can tell your units COP by using the equation COP equals the quotient of energy output and energy input. The measuring unit of amount of heat moved is the BTU, British Thermal Units per hour. The energy, on the other hand, is measured in watts. And 1BTU equal to 0.293 watts. 

For instance, an air to water heat pump energy output is about 60,000BTU. It also runs at 42000 watts. To get the units COP, multiply the BTU by watts (60,000 X 0.293. Which should give you 17,580.). So, the energy produced is 17,580 watts when moving air from indoors to outdoors or vice versa. Then divide the output watts by input watts 17,580/4,200. That gives you 4.18 COP.

Ways that you can better your HP's COP

Air to water heat pumps COP can be improved by decreasing the hot and cold temperature gap by which the unit runs. Since air to water heater pumps is two-way round- heating or cooling, you have to reduce the output temperature. The new reading should be 30 °C. You have to use oversized canals, piped floors, walls, or ceilings to reduce noise. On the other hand, the input temperatures should be increased. You should use groundwater instead of air in this front.  

The heat pump can be improved if the internal heat exchanger sizes are increased. Consequently, this increases efficiency in line with the energy used by the compressor since it reduces the unit’s internal temps difference over the compressor. 

COP of absorption chillers can be increased by using a second stage or a third stage. dual and tripled effect chillers are super-efficient compared to single effect coolers, with COPs exceeding 1. They demand high pressures, super-heated steam, yet it’s still a fairly a slight ten quid of vapor per 60 minutes per ton of cooling.

Factors affecting coefficient performance 

Air to water heat pumps absorbs heat and discharges it into the earth or water in the summers. In the exterior air, an air source performs the same thing. An air to water heat pumps easily extracts and discharge heat. This is due to the warmer ground temperatures in winter and cooler in the summer seasons.  

Despite this, some factors may hinder its performance, such as:

Type of the air to water loop

The greatest COP is usually associated with open-loop heat pumps. On the other hand, the closed-loop will have relatively fair COPs but not as much as the open one. 

Purpose 

As with many geothermal heat pumps, they work best in cooling mode and not heating. 

Is it running on high stage or low stage?

Geothermal heat pumpshave a two-compressor feature. Less energy is consumed when only used in the lower stage. So, the COP of the heat pump gets high while it's on the low stage. 

The exterior temperatures

The temperature outside has a big impact. For instance, if the heat pump conditioning your home's air and the temperature outside is 80 F and 70 F, the gap is ten degrees on the inside. It's pretty simple to disperse the heat at 80F. However, if the exterior temps reach 110 F, the heat pump has to strain further and use more energy, reducing the COP. 

Wrapping up 

In retrospect, a good COP for an air to water heater pump should be above 4.0. nevertheless, there are still other factors at play. What's the type of lop on your air to water eater pump? Are you running it in cooling mode or heating mode? Are you using the high stage or lower stage? In general, a heat pump can run on a COP of 4.7+ provided it's optimally operated.