A heated discussion on heat pumps

A heated discussion on heat pumps

The water heat pump market is growing from the requirement that 50% of energy in developments derive from alternative energy sources, stipulated by SANS standard 10400-XA. Rising demand for energy-efficient buildings and innovative water heaters is negating the need for traditional energy-guzzling geysers.

By Eamonn Ryan

Heat pumps use substantially less electricity to heat water than do resistance heaters such as geysers – by how much, depends on their particular technology. All heat pumps have to declare their coefficient of performance (COP). In South Africa, because of high ambient temperatures of the surrounding air, an air source is used to heat water, whereas in many northern hemisphere countries, they draw heat from many other sources.

James Vermeulen, Electrolux product manager: Green Energy, says any need for changes to the design of a building to accommodate heat pumps, stem from their requirement for good ventilation to function – preferably on a roof. If anywhere else, such as a duct, provision has to be made for adequate ventilation, or the system will not work. “Without ventilation, the outgoing air will be the same temperature as ingoing.”

Mines are major adopters of heat pump technology. The 20-year lifespan of heat pumps and modular design means that when a mine runs out of ore, it can simply lift the heat pump and relocate it at another mine. Mines utilise extremely large heat pumps due to the demand for substantial volumes of hot water in their staff shower-houses.

Large heat pump located at Sun City. Image by SolahartHeat pumps come in two forms: as a split pump with an external attachment to the tank; or an integrated pump where the two are combined. In a residence where there is an existing geyser, it can be retrofitted to accommodate a heat pump. Although the savings on monthly electricity mean the residential pay-back period may be 18 to 26 months, the retail market tends to find this too long. Furthermore, it requires annual maintenance which adds perhaps another month a year to the pay-back. With Eskom’s rebate programme that had temporarily reduced.

Performance criteria

“The most important effect of the performance of a heat pump is the planning and design of a heat pump system,” says Sascha Altmann, managing director: Stiebel Eltron Southern Africa. “In a proper heat pump plan, you have to consider two very important facts: the input- and the output-parameter. The input parameter consists, for example, of the ambient conditions that the system has to operate within, such as temperature and humidity, which have a great impact on performance. The output parameter describes the requirements of the specific project, like the amount of domestic hot water required; is space heating or space cooling required via the heat pump; or does the client want to heat his pool with the same device? Also the intelligence of the heat pump controller is important. You need an intelligent controller that runs the system in the most effective way. And last but not least, the installer has a significant influence on the performance. A heat pump is only as good as its installation: Pipe distances must be kept as short as possible; and the pipework needs a proper insulation to avoid energy losses. All this influences the performance of a heat pump and the efficiency you can get out of the system.”

Grant Spires, maintenance manager at GMC Aircon outlines some other factors that can affect the performance of a heat pump. “Lime scale build up in the shell tube heat exchanger can reduce heat transfer into the water, which in turn will have a negative effect on the COP of the heat pump unit.”

Certain processes can be undertaken in the manufacturing or installation process to extend the life of the equipment. “Stainless steel sheet metal can be used in the manufacturing of heat pumps, and evaporator coils can be chemically treated to extend the life span of heat pumps placed along coastal areas. Servicing of heat pumps is very similar to that of an air conditioner’s condenser (outdoor unit). Coils and drain pans need to be kept clean and the usual electrical and refrigerant checks need to be carried out. The system is self-contained (such as with a fridge) so one should never really have to adjust gas pressure unless there has been a gas leak. Most of the maintenance and repairs would be carried out by an air conditioning technician,” says Spires.

Altmann adds, “For heat pump manufacturers it´s important to take the wide range of temperature difference in South Africa into consideration. Heat pumps must be able to work in conditions between -10°C and +42°C outdoor temperature, otherwise the system will keep tripping or running purely on the element. Furthermore it´s important that the heat pumps are protected against corrosion in the coastal regions, as the salty air is very aggressive and can cause corrosion. As we have a high demand for cooling in summer, the heat pump should also be able to cool, so that the client can use one device for his domestic hot water heating, space cooling and pool heating.”

In addition, ambient air temperatures also affect the COP of the unit, says Vermeulen. “The higher the air temperature, the better the performance will be. When the system gets tested at SABS and test laboratires they test it over a spectrum of -0.5°C to 40°C to get an average COP of the system. Where a heat pump is deployed in an extremely hot location it has a safety feature whereby when the combined temperature of the water and the system gets above a limit of 90°C, it automatically switches off to protect the compressor from overheating, until it cools down.”

Altmann adds, “To install a heat pump system, the building must have a central plant room where the storage water tanks as well as accessories like circulation pumps can be placed. The heat pump can be placed in this plant room. It can be connected with air ducts to the outside, so that the system will get enough fresh air as energy source and can blow the exhaust air out again. Another possibility is to place the heat pump installation outside, in which instance the building has to offer enough space for such an outdoor installation. To supply the hot water to the different points of use, it´s recommended to run a ring main through the building, to serve the client with immediate hot water and avoid waste of water.

“A heat pump would typically mainly be recommended by consulting engineers, but is also picking up on the contractor side of the industry. For a domestic application, a consultant is not necessary, but with industrial or commercial I would say consultants are needed and both consultants and contractors should work closely together to make sure that both understand the hot water design and also the function of the heat pump. Examples of common pitfalls are: not understanding the application and its hot water demands and then undersizing the hot water storage (vessel); the sizing of the heat pump according to size of storage; and recovery times of the water for the next draw of hot water.”

Vermeulen says the architect and consulting engineer should jointly be involved from the beginning in designing the service ducts to accommodate the system, “especially if the heat pump is to be located in the basement of a large commercial building, to ensure adequate ventilation.” Wet services engineers need to be involved to ensure the correct pipe sizing and installation is correct, he adds.
As to what it takes to grow the heat pump market, Vermeulen explains that regulations require that 50% of water heating come from alternative energy sources – typically heat pumps, solar energy or gas. He says whichever is specified depends on the circumstances and design of the building. “In some instances, solar will simply not work and a heat pump will be specified. But there’s a place for each in the market. Solar heats up the water during the day, but once it’s used, the system defaults to electricity. With heat pumps you save two-thirds of your electricity, have hot water all the time and you don’t have to provide for bulk storage, which you do with solar.”

The pay-back time for a heat pump compared to alternatives is highly variable, says Vermeulen, as it depends on hot water usage, ambient air temperature and the COP of the actual device. It is commonly accepted as being lower for industry and commercial buildings, Spires says 12-18 months, while others say 18 to 24 or even 35 months for domestic heat pumps.

Altmann says, “Of course the pay back time for heat pumps is dependent on many influencing factors, like hot water consumption. To give you an example, for a standard three-person household with showers, bath tub, kitchen- and handwash sink, the amortisation will be with 4-5 years. The savings that you can create in such a case with a heat pump, can be up to R70 000 within a 10-year period.” To calculate the estimated return of investment for your specific application, Stiebel Eltron offers a tool, that you can download online, at: https://www.stiebel-eltron.co.za/toolbox/tools/?excel.

Advancements in technology are being made all the time, but the pricing has not reduced due to the impact of the exchange rate. In hard currency terms, says Vermeulen, the price has come down to the exent that prices have not increased in recent years even as the exchange rate has considerably worsened. “For the same amount of money, today you get a lot more advanced technology than what you would have had in 2010, when Kwikot first started importing heat pumps. For instance, heat pumps that heated water to 55°C now heat it to 75°C, the same as what you would achieve with a resistance element – for a third of the energy.”

Major projects

Sun City in the North West includes four hotels including two five-star hotels. Sun International wanted to reduce its impact on the national grid and work towards Eskom’s aim of reducing demand by 10%, while maintaining aesthetics and avoiding noise pollution.

Sun City is one of many other commercial operations who have opted to install heat pumps either for environmental or economic reasons. In what is one of the largest such projects in the country, seven HW80-3s were installed at the Sun City Main Hotel, six HW20-3s at the Cascades Hotel, two HW60-3s at the Sun City Cabanas and three HWW80-3s at the Palace of the Lost City.

The hot water requirement was for 428 000ℓ/day at a temperature of 60°C, for an estimated energy saving of 1.28 GWh/year.

Three air-to-water heat pump exchanger setups and one water-to-water heat pump exchanger setups were installed to heat 48% of the daily demand. Solahart designed a solution that it says is unique to southern Africa: a water-to-water heat pump system including the plant room and piping for the Palace of the Lost City was installed. The water-to-water heat exchanger helps to heat the 80 000ℓ/day of 60°C water that the Palace of the Lost City requires. Three air-to-water heat exchanger solutions heat the 60 000ℓ/day, 40 000ℓ/day and 50 000ℓ/day of hot water for three hotels respectively. The project resulted in a demand reduction of over 650kW.

A corporate office-sized heat pump. Image by SA Heat Pump EngineersVaughan Boultwood, Rhem Australia Regional Sales and Marketing Manager, explains, “A weir was built to dam the water from the river so that we could use the thermal energy from the water and with a 5°C differential maintain the heat in the pool to around 27°C without a pool cover. We replaced a 900kW electric boiler which was used to heat the pool.

“The hotel did not want a noisy ‘air to water’ heat pump and as the pool plant room was located near to the pool, though hidden. It was best that a ‘water to water’ heat pump be used, which is much quieter and has a higher COP of 7.5. This was the case for the main hotel where we took thermal energy from the lake next to the hotel and with a temperature differential of 5°C we were able to generate about 58°C using three 80 kW ‘water to water’ heat pumps to pre-heat four 20 000ℓ electric boilers, raising the Delta T of the water by 40°C and therefore providing significant energy savings for the hotel,” says Boultwood.

A plumber’s perspective Johan van den Berg, Burgess Plumbing’s Business Development Manager, though also a plumber who regularly installs heat pumps and solar water heaters, says his experience has led him to present customers with all the information, encourage them to do their own research and to make their own informed decisions – rather than try lead them in any direction.

“Once they’ve decided, I then give my input on what would be the best solution for their actual site, their needs and requirements. One of the most basic misunderstandings when people hear of a 3kW heat pump, is that it’s the same as a traditional geyser: in fact, this refers to the output rather than electricity consumption.” A 3kW heat pump can comfortably heat 250ℓ water. When it comes to choice of equipment, Van den Berg says he typically recommends local manufacturer MTech Industrial’s Enerflo brand, which delivers high temperature hot water for the same energy; and in the high-end commercial space, Stiebel-Eltron.

Altmann says, “We´re able to deliver complete solutions for domestic hot water heating, space heating, space cooling and pool heating from one device. We have already completed several installations in South Africa with heat pump systems in combination with a thermal solar solution and achieved fantastic COPs with our products. We´re also able to integrate the heat pump system into a building automation, so the client has the possibility to control and monitor its heat pump centrally. Of course the client can also connect the heat pump to the WiFi and use his smart phone or tablet as a remote control. In service cases he also can grant our technicians access to his heat pump via the internet, so that we can deliver immediate support and check the system online.”

In the residential market, the major demand is to retrofit existing geysers with heat pumps, disabling the geyser’s element. The geyser simply becomes a water tank, although with Enerflo the element remains enabled and can in need to activated by a remote.

Van den Berg attributes heat pumps not being more commonplace, to the same sort of negative perceptions as bedevilled solar heaters before it: substandard products were imported and often shoddily installed by unqualified crews, resulting in defective performance and disillusion.

The solar heating market was hijacked by government, or Eskom, and this left a bad taste among responsible homeowners who opted to go ‘green’. “For instance, the scaling of systems was not done as per SANS requirements.” He has been called out to service substandard systems sold for premium prices, whereas the company or resident could have bought a premium product for the same price.

The pumps require regular service in the same manner as does a car: without it, the COP will steadily worsen and the system ultimately fail – like a car. A basic service requires descaling of the heat exchanger, cleaning out the condenser to ensure no build up of residue and checking the condition of the heat pump’s components, levels of gas and inspecting the pipe insulation.

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