About Heat Pump Technology
Heat Pumps are widely used all over the world to heat water.
What is a Water Heat Pump?
A heat pump is a device that uses a compression vapour cycle, similar to that used in
fridges and air conditioners to heat up some sort of fluid such as water. There are two
main types of Heat Pumps – air to water and water to water. We will focus on air to
water Heat Pumps. Simply put, the heat found in the air is transferred to the water
through three key components – an evaporator, a condenser and a pump. The Heat
Pump is therefore mounted in a well ventilated area where the heat exchange process
can take place. Heat pumps are used in domestic, commercial and industrial
applications and are accepted worldwide as the number one water heating technology
(According to the French conference on energy efficiency). Heat Pumps are common
in Europe, Asia and the Americas as energy efficient water heating devices. Due to
their higher initial installation cost, they have not been as widely used on the African
continent.
The following pictures show what a Heat Pump looks like in various sizes:
Industrial Water
Heat Pump
Commercial
Water Heat
Pump
Domestic Water
Heat Pump
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
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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.
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 Heat Pumps:
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Pro's Con's
75% Energy Savings Achievable Operational noise level
Well established technology Higher initial capital outlay compared to
other water heating systems
Simple installation in either a new
application or retro-fit.
Needs well ventilated area
Low maintenance required Operation in extremely cold
environments (<-10˚C) problematic
Not dependant on the weather for
operation
Calcium build-up in water can lead to
extra maintenance
Good return on investment Not well established in South Africa
Cold air as a bi-product
Small installation foot print
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.
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As can be seen in the above table, specialised attention is only required every 20,000
hours and this is typically done by an air conditioning professional. All other
maintenance must be undertaken as would be normal with current electric boilers.
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. The following table shows the comparative
differences between R417A and R134a.
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No. Name:Chemical Formula
or % mass mixture:O.D.P.:
G.W.P.:
20; 100; 500yrs
Safety
Classification:
R134a Tetrafluoroethane C.F3.C.H2.F 0.0 3,300; 1,300; 400 A1
R417A HFC Blend HFC-125 (46.6%)
HFC-134a (50%)
HC-600 (3.4%)
0.0 4,400; 2,200; 700 A1/A2
O.D.P. referenced to Ozone Depletion Potential of CFC-11 (i.e. O.D.P. of
CFC-11 = 1.0).
G.W.P. referenced to the absolute global warming potential for CO2 using time
horizons of 20, 100 and 500 years. The bold figures refer to the 100 year time
horizon commonly used as the inventory standard. Calculated GWP values
for refrigerant blends have been rounded to the nearest 100.
SAFETY GROUP CLASSIFICATIONS as noted in AS 1677 part 1 are
indicated by alphanumeric characters (e.g. A1, A2, B3 etc). The capital letters
A or B indicate lower or higher toxicity respectively and the numeric value
refers to the refrigerant’s flammability (the number 1 being no flame
propagation and 3 being higher flammability).
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.
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Heating
Type
Calorie /
kWh
Energy /
Perf.
Ratio
Unit Price
Required
Energy /
ton of
water
Required
Cost / ton of
water
Labour Cost Coverage
Annual
Operational
Cost
Coal
Boiler
4000kcal/kg 40% $0.08/kg 25.10kg $2.32 $5,128 20m3 $12,641
Oil Boiler 8429kcal/kg 80% $0.6/l 6.40l $3.84 $5,128 20m3 $19,141
Liquified
Gas
10800kcal/kg 73% $0.85/kg 5.30kg $4.48 $2,564 10m3 $18,936
Solar
Electric
860kcal/kg 85% $0.09/kWh 51.6kWh $1.92 NO 150m3 $7,028
Electric
Boiler
860kcal/kg 90% $0.09/kWh 51.6kWh $4.63 NO 10-15m3 $13,487
Heat
Pump
860kcal/kg 400% $0.09/kWh 13kWh $1.17 NO 3-10m3 $4,256
Graph of the above data shown visually below.
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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.
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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 -5˚C and 40˚C, 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.
Installation of Heat Pumps
Heat Pump installation, while simple at a glance – are engineered solutions. Many
factors are taken into account before an adequate Heat Pump can be recommended.
Since a Heat Pump comprises of a compressor, evaporator, fan, piping and valves,
each component must be matched to the required solution. In addition to the internal
components of the Heat Pump, other external factors are calculated. Water Storage
Tank size, number of tanks, water flow rate, external pump specification, volume of
water used, water temperature required, unit mounting and location are but a few of
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the elements used in the calculation of the specification. Although there are many
ways that a Heat Pump installation can be engineered, the most common installations
fit into two main categories as follows:
New Installations
A new installation usually occurs in the design phase of a building project. The Heat
Pump engineers will work closely with the architects and designers to provide the
perfect solution matched to the application. Water usage, ventilation, pipe length,
water tank size, location and insulation are just a few of the variables considered
when designing the correct solution. The Heat Pump specification once complete will
be included in the final design for production. The following diagram shows a
simplistic simulation of a typical installation. A Heat Pump is not always installed in
this manner and it should by no means be seen as a blueprint for installation. In most
industrial and commercial applications, more than one water storage tank is used and
they could be connected in series or parallel, in addition, multiple Heat Pumps may be
installed to produce the required result.
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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.
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