The Difference Between True Heat Pump and Heat Pump like AC Units

The Irish heat pump market has dramatically increased in the last couple of years for a number of reasons; Climate change, CO2 reduction commitments of EU countries and the fact that Ireland is committed to catching up with other members of the EU, the market will continue to grow. Heat pumps are reliable and undoubtedly one of the best ways to meet those targets especially with Ireland’s renewable electricity potential from wind and PV increasing annually. However, is there enough general knowledge about this “NEW” technology from public sources, heating design professionals and renewable companies to make the right choices and decisions?

From our experience in the Irish market over the past decade and with in-depth knowledge about other European countries, the answer is no. Most EU countries (especially those with colder climates) have been developing and fine tuning the technology for the past two decades. It is therefore no surprise that the true heat pump brands are much more popular in countries like Sweden, Denmark, Germany, Czech Republic or Austria than their “dressed up” Air conditioning unit rivals.

There are a number of reasons why many citizens and trade professionals from these countries have learned the hard way by installing a “budget friendly” units and several years later they find themselves forced to do it all over again using real heat pump technology.

As MasterTherm Ireland is an Irish based company, with partner businesses spread all over Europe, as well as a direct relationship with the manufacturing team in the factory in the Czech Republic, we would like to summarise facts and hopefully protect our Irish customers.

System Design

Heat pump system efficiency is determined by a number of factors: the quality of the compressor, the expansion valves, the dimensioning of heat exchangers, the quality of control system, size of evaporators etc.

Traditional air conditioning systems (often referred to as “air-air heat pumps”) are developed and manufactured for cooling as their main purpose, where the difference between primary and secondary temperature is between 15 – 20 °C (for example outside air 35°C, supplied chilled air 15°C).

The construction, controls and dimensioning of such units is specified and built to satisfy these requirements and can also potentially reverse the function, supplying warm air when in heating mode. However, that is not it’s primary purpose and if these are continuously used as a heat source, the life span reduces dramatically. It is disturbing to see Irish authorities using these lesser quality models as a heating solution for social housing.

For both AC units dressed up as air-water heat pumps or true heat pump systems, the task is harder. Heat from refrigerant is passed to water and then via emitters to indoor air.

The difference between primary and secondary temperature is commonly as big as 50 °C and higher. For this reason, quality of components, optimal dimensioning and level of control is completely different for true heat pumps as it is essential for efficiency and the life span of system, built for heating rather than cooling purposes.

Undersized or unsuitable components

It is often the case that invertor-driven unit components are designed for average, NOT maximum load. When such a system is under higher heat load, effectiveness of the heat source drops dramatically. Overall efficiencies are then below average when compared to a real heat pump.

One stand-alone issue of all “fake” heat pumps is the evaporator (often still called condensers from the AC set up). The spacing of fins is typically 0.8 – 1.2mm, which is much smaller than on genuine heat pumps.

Units then have to defrost much more frequently (especially in Irish humid winters) as the small gap between evaporator fins fills up quickly with freezing condensate.

The amount of defrost cycles is multiple when compared to heat pumps with fins spacing 2 mm and more. Time of defrosting cycle of these units is relatively short but regardless of that, the impact on efficiency is often significant.

Much more serious is the fact that the evaporator is exposed to many more heating/cooling cycles, thus increasing thermal fatigue and significantly reducing the lifespan of the evaporator.

The evaporator example is only one of many.

But why would multinational corporations manufacturing these products not address this issue? There are a number of good reasons.

Bigger spacing means lower energy transfer per cm2 of the evaporator. To get the same energy transfer would require an increase in the size of evaporator. If the spacing is optimised for defrosting cycles and correct energy transfer, 1 Meter tall condenser/evaporator will increase to 2 meters high. Consequently the size of housing of the unit would also have to be increased.
Existing condensers manufacturing plants could not then be used or would have to be modified to produce HP evaporators.
Exiting housing manufacturing would have to be optimised also.
These adjustments would increase the cost of each unit as more materials, energy and labour would have to be used.
Shipping and storage costs would also have to increase dramatically as many AC heat pumps are shipped half way around the world.

The evaporator/condenser is just one of many issues that the converted AC units are facing. But how are they then achieving similar COP/SCOP laboratory testing results as real heat pumps? Well there are a number of answers to that but that is a whole other article. We will however briefly touch on that topic below.

AC is not a heating system but a heat source

Prices of AC units (dressed up as heat pumps) are often very attractive at first glance and are directly linked to high quantities of serial manufactured pieces. Of course there are much higher numbers of AC units sold globally annually than heat pumps, and it is therefore attractive for AC manufacturers to modify these for heating purposes.

For this and other reasons, the price looks much more favourable. However, these are not (as are often mistaken) heating systems but only heat sources. Installation companies then have to design the rest of the system e.g. Bivalent source and it’s controls, circulation pumps, controls of heating circuits, controls of DHW, integration with solar panels, weather compensation control of circuits etc. All this and more is in the hands of installation companies (often plumbers or electricians)

Once all of these components are added to the price of the heat source, the original price favourability often disappears. Most importantly of all, the manufacturer of the heat source never guarantees functionality or efficiency of the heat source and it is mostly the installer who takes the blame.

Typical is an example of absence of MaR and units working in heating zones on/off regime defying the purpose of invertor driven systems or “system link” type controls, switching zones on on/off bases. In the case of commercial application, it is more or less guaranteed that the building, including the heat sources are controlled by some sort of BM system. Heat sources are also just being switched on or off based on time clocks, completely defying the basic rules of heat pump technology. In contrast, purchasing a “true heat pump” will guarantee functionality, including a control system that is synchronised with the building, all heat sources and emitters thus achieving much higher “real life” efficiency and longer life spans.

Lifespan of heat pumps

The lifespan of average AC units is around 5-7 years. The lifespan of purpose-built heat pumps is somewhere between 15-20 Years, depending on the nature of use and application. (A heat pump working on a commercial application such as a swimming pool, working 24/7 365 days a year is likely to have a shorter lifespan than system used mainly in the heating season)

In order to achieve such a long lifespan, heat pumps and especially outdoor units have the following features:

Robust, rust resistance aluminium or stainless steel frame and panel
Water and dust sealed electrical/ control compartment
Evaporator fans with extended lifespan
High quality invertors
All mechanical, electrical, and refrigeration components have to have easy access for maintenance and possible replacing.

Most AC type units labelled as heat pumps, lack the majority if not all of the features listed above.

COP – Coefficience of performance ,
SCOP – Seasonal coefficient of performance </h2

Coefficient of performance is the holy grail of all heat pump distributors. But very few are ready to explain all of the conditions under which these results are achieved. (A7W35 is far from the real testing rules) The Norm EN14511 allows a range of accuracy up to 15%. Manufacturers are also allowed to set defrosting periods and many other tricks are used to get the desired results. It is very much up to manufacturer to have honest results or results optimised for an easier sell.

SCOP, EN14825 is a much more sophisticated way of testing, and considers heating water temperature which is directly linked to climate conditions and degree days different for each European climate zone, system sizing towards to heat loss of the building, bivalent source, speed etc.

Unfortunately, this norm is not used by Irish representative body SEAI to state efficiencies of heat pumps. SPF – Seasonal performance factor (dedicated figure of already vague COP results) is used instead.

Regardless of what is being declared by the manufacturer, the “brochure” and real life efficiency can be very different when connected to heating distribution system.

The efficiency of the complete system including plant room, emitters, controls etc. is therefore much more important than efficiency (COP/SCOP/SPF) of the heat source.

A key for efficiency is the overall design of heat source together with plant room and heating distribution system, quality control system and correct control strategy.

Summary of steps how to differentiates modified AC units from real heat pumps

Check in product technical list or data plate of the outdoor unit.
If manufacturer/distributor refers to the outdoor unit as a “condenser” instead of evaporator, it is very likely an air-conditioning unit is being used as a heat pump evaporator.
Check spacing of evaporator fins.
Spacing smaller than 2 mm is likely to be AC.
Over all physical size of the outdoor unit.
Too compact outdoor units are unlikely to have minimum spacing of evaporator fins. If the manufacturer produces AC units as well as heat pumps, check the manufacturers AC range. If the condenser’s physical size from AC range matches the size of the evaporator of “heat pump” it is not an evaporator but a converted AC condenser.
Check on the service access.
Restricted access to mechanical parts means dramatically shorter lifespan.
Check on availability of official laboratory test report.
Avoidance of manufacturers providing these reports usually leads to the conclusion of much lower efficiencies than stated in the product advertising brochure.
Check if the heat pump comes with full control system, possibly built in bivalent source, interaction with other heat sources ( solar panels etc.)
AC units almost never have built in bivalent heat sources as they are design to chill not to heat.