How does a Water Heat Pump Work?

A refrigerant fluid is pumped around in a circuit where it evaporates on one side of the circuit and condenses at the other. Evaporation absorbs heat whilst condensation releases heat. In a heat pump, heat is absorbed into the refrigerant fluid by the evaporator at one side of the circuit, the fluid is pumped around to the other side of the circuit where the absorbed heat is released in the condenser. To most people heat pumps will look very similar to an air-conditioning or refrigeration units because they are very nearly identical, with the only difference being the roles of the condenser and evaporator are used for different functions.


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Commercial Heat Pump
Industrial Heat Pump
Domestic Heat Pump
Domestic System
Heat Pump Diagram
What are the Benefits of using Water Heat Pumps?

While the product does have some draw-backs which are listed below, the fantastic advantage they do have is their ability to produce heating power at a fraction of the cost of other technologies. Many studies and comparisons have been done to show the energy saving capability of the product. In most of these studies the savings average at between 60 and 70%. A recent study commissioned by Eskom was carried out by the University of the North West which found the same overall result. Water Heat Pumps although not a new technology have been identified as one of the foremost products needed worldwide for energy saving.

The following table shows the Pro's and Con's of Water Heat Pumps:
Pro's
Con's
  • 75% Energy Savings Achievable
  • Well established technology
  • Simple installation in either a new application or retro-fit
  • Low maintenance required
  • Not dependant on the weather for operation
  • Good return on investment
  • Cold air as a bi-product
  • Small installation foot print
  • Operational noise level
  • Higher initial capital outlay compared to other systems
  • Needs well ventilated area
  • Operation in extremely cold environments (<-10C) problematic
  • Calcium build-up in water can lead to extra maintenance
  • Not well known in South Africa
Maintenance on Heat Pumps

A maintenance table below describes the measures that need to be taken to ensure long life and maximum efficiency. The table should be used as the basis for any maintenance schedules that need to be compiled and given to the maintenance staff. The typical lifespan of a Heat Pump should be in excess of ten years and although very little maintenance is required, regular checks should prevent possible damage to the unit and prolong the life of the Heat Pump. Typical maintenance staff might comprise of plumbers, electricians and air conditioning professionals. The only addition to the list of maintenance staff when compared with electric boilers (geysers) is that of an air-con technician.

Heat Pump Gas Specifications

Heat Pumps require a refrigerant to complete the vapour compression cycle. The Deron Heat Pumps that are installed by Light and Sensor use R417A which is a blended gas. It is directly interchangeable with R22 as it is considered the replacement gas for R22. In South Africa, R417A is less commonly used and more expensive than R22 or R134a. Although it is the choice of most manufacturers, Heat Pumps can be run on either of these gasses. R417A can be interchanged with R22 if not available, however under normal conditions, the need to re-gas or change gas is not necessary. The gas should not need replacing during the lifespan of the unit in most instances and if the need arises to do this, we recommend R417A be used. Although R134a can also be used with some initial modification to the Heat Pump, it will change the specifications of the Heat Pump unlike R22! Typically, R134a is only used when higher than normal tank temperatures are required. We do not recommend this as it is not common and not necessary.

Comparison with Other Existing Technologies

There are six main technologies used worldwide for water heating; Electric Boilers (Geysers), Coal Boilers, Oil Boilers, Liquefied Gas, Solar Electric and Heat Pumps. The table below shows the six types of technology compared. This information in the table has been extracted from one particular report compiled in China. There are numerous reports that compare water heating technologies, most of which come to the conclusion that Solar Water Heaters and Heat Pumps are by far the most energy efficient. Unfortunately Solar Water Heaters do not have a good commercial application as they require a large amount of space at a high cost.
The following two simulated graphs are an extract from the Eskom report compiled by the university of the Northwest. The simulation shows that Solar Electric systems slightly out-perform Heat Pumps in a residential environment. They also show that the payback period for Heat Pumps is better than that of Solar - again in a residential environment. Typically, most Solar Electric installations are residential because of the amount of space needed to produce adequate heat. In a commercial application, Solar Electric systems can become very expensive and cumbersome to install. For this reason, Heat Pumps have found majority of their market in commercial and industrial environments. These types of installations include, hospitals, mines, apartment blocks, hotels, offices and similar.

Heating Type
Calorie / kWh
Energy /
Perf. Ratio
Unit Price
Requ'd Energy /
ton of Water
Requ'd Cost /
ton of  water
Lab Cost
Coverage
Annual
Oper. Cost
Coal Boiler
4000 kcal/kg
40%
$0.08/kg
25.10/kg
$2.32
$5 128
20m
$12 641
Oil Boiler
8429 kcal/kg
80%
$0.61/kg
6.401
$3.84
$5 128
20m
$19 141
Liquefied Gas
10800 kcal/kg
73%
$0.85/kg
5.30/kg
$4.48
$2 564
10m
$18 936
Solar Electric
860 kcal/kg
85%
$0.09/kWh
51.6kWh
$1.92
NO
150m
$7 028
Electric Boiler
860 kcal/kg
90%
$0.09/kWh
51.6kWh
$4.63
NO
10-15m
$13 487
Heat Pump
860 kcal/kg
400%
$0.09/kWh
13kWh
$1.17
NO
3-10m
$4 256
Heat Pump Comparison Chart
The graph depicted below was compiled by the Plumbing Industry Association of South Australia. The results of their report show that the Heat Pump out-performs the Solar Electric system - again in the residential sector.

Why the variance in results from report to report? Firstly, Heat Pumps are fairly consistent and are not normally affected by weather. Cloudy and rainy conditions produce less efficient results for Solar Electric systems whereas these factors do not reduce the efficiency of Heat Pumps as drastically. The reason for this is that the Heat Pumps COP (Co-efficient Of Performance) is directly related to the ambient air temperature. Most Heat Pumps operate comfortably in temperatures between -5C and 40C, which means their COP values in general fluctuate between 2 and 6.

In some instances where the ambient air temperature does not permit the use of an air-to-water Heat Pump, water-to-water systems can still be used. South African conditions are perfect for Heat Pump installations because our ambient air temperatures are generally high throughout the country and throughout the year.

Payback Period vs Solar
Geyser vs Heat Pump vs Solar
Retro-fit Installations

Retro-fitting of Heat Pumps to existing installations is very common since both corporates and end-users are either required by law to look at energy efficient (or environmentally friendly) technologies or there is a requirement to save on running costs. The term retro-fit implies that the Heat Pump (in this case) is installed to an existing solution for water heating. The most common retro-fit occurs where clients have an electric boiler (geyser) which needs to be retro-fitted with a Heat Pump to replace electric element heating. As is common with the new type installation, design and engineering is critical to the success of the installation. In most cases, retro-fitting designs are more complex since buildings may not be designed with adequate ventilation, insulation and so on What is also common practice as part of a retro-fit is the continued use of the existing electrical elements as a back-up means of heating the water. The following diagram shows one possible simplistic retro-fit solution. Again, it is not a blueprint and rather a visual representation.