Collaboration on DHW (domestic hot water) heat pump broadening ambient boundaries
One of the highlights of the parallel heat pump session at ATMOsphere Europe 2015 was ENEA’s (Italian national agency for new technologies) ongoing four-year case study of CO2 and hydrocarbon heat pumps for domestic and commercial applications in European conditions. The European project, including three universities (Stockholm, Napoli and Valencia) and several manufacturers including Alfa Laval, Dorin, Danfoss and Lu-ve, was designed to test three R290 heat pumps and two CO2 heat pumps.
To date, ENEA have performed around 80 tests set to international standards. Raniero Trinchieri outlined the project, which commenced in December 2012, including the development of a new 30kW CO2 heat pump for residential heating of hot water as well as a 50kW commercial heat pump. As part of the joint project, Enex is supporting the design and construction of heat pumps and control of the machine, Dorin (compressor), Lu-ve (CO2 heat exchangers), Alfa Laval (gas cooler and internal heat exchanger), and Danfoss (electronic expansion valve).
“This (30kW heat pump) can work in a range of ambient temperatures, which is not conventional for a CO2 heat pump as it utilises a two-cylinder compressor,” Trinchieri said of the results.
Indeed the heat pump for domestic applications has proven to work in winter (-10°C to 10°C) and summer conditions (20°C to 35°C) producing 60°C hot water (up to 80°C capacity). The 50kW heat pump for commercial purposes functions in an ambient range (-10°C to 35°C), producing 80°C hot water.
“After testing we have evaluated the global performances of the heat pump,” Trinchieri said. “For example for compressors and gas cooler the performances were good for most operatic conditions. We had some problems with the internal heat exchanger and evaporator; the internal heat exchanger had efficiency problems due to the the high temperature of the evaporator, which was higher than expected, in particular when the ambient temperature increases.”
Trinchieri noted that performance in terms of COP is greatly improved when the ambient temperature is higher than 2°C. To improve further in this area the project partners are focusing on three key areas:
- Optimisation of gas cooler pressure by internal control
- Optimisation of the internal heat exchanger efficiency
- Optimisation of work conditions of evaporator
Dorin is working on improving the compressor, which is already showing ‘high mass flow and high input power in many operating conditions’ but ‘the electric motor, suction reeds, valve plate and discharge port have to improve as well as the controller of the gas cooler pressure’.
“This is because in some conditions, when the ambient is higher than 20°C and water inlet temp is higher than 30°C, the controller does not work in an automatic condition,” Trinchieri said.
boostHEAT’s integrated heat pump/boiler a ‘global solution’
Michael Miranda of boostHEAT presented a new type of natural gas-fuelled residential CO2 heat pump. The heat pump has been shown to increase efficiency by up to 200% in light of the fusion between the boiler and heat pump.
“The innovation of the heat pump boiler is really the fusion of the boiler and the heat pump into one fully integrated unit and this is achieved by our patented thermal compression technology,” Miranda explained.
At the heart of the technology is the new thermal compressor, which uses the heat from the burner instead of mechanical energy, to efficiently compress the natural refrigerant. The compressor activates the thermal compression cycle at a high temperature. The pressure cycle is the direct result of the thermal cycle, which has the added benefit of causing minimum wear to the equipment.
French gas distribution company GDF SUEZ helped with testing the product and the results showed an efficiency of 200%, COP 5.2, producing 35°C water temperature. Impressively, even at a very high water temperature (65°C) the efficiency was 165% with a COP of 4.29. The unit reaches a capacity of 22kW at -10°C ambient and 33kW at 7°C. Here, the boostburner can add additional output if needed; it runs at the efficiency of a condensing boiler, which is integrated into the thermal compressor.
“We see (the heat pump) as a solution for the global residential heating and hot water market,” Miranda explained. “We’ve been able to achieve a real leap forward in efficiency really by taking advantage of the full benefits of our natural refrigerant carbon dioxide.”
The heat pump boiler is designed for homes (new and replacement for old models), providing heating and hot water all from one unit. The second generation of the ‘combination boiler’ is already underway, with at least five units to be installed in France in 2015. boostHEAT will conduct further testing in the UK, which it sees as a viable market for the product.
Q-Ton making inroads in Europe with industry high COP of 4.3
Shigeru Yoshida of Mitsubishi Heavy Industries (MHI) presented a number of case studies on its Q-ton CO2 heat-pump water heater. The Q-Ton has been successfully installed in a range of applications in Japan and Europe, achieving efficiency gains and operation at an ambient temperature as low as -25°C, with an industry-high COP of 4.3. As was outlined at ATMOsphere Asia 2015, the transcritical heat pump initially faced the same challenges as its predecessors in cooler temperatures, but MHI has been able to improve its performance in very low ambient temperatures.
The Q-Ton is a specialty heat pump for domestic hot water applications and Yoshida noted the differences in installation between Japan and Europe.
“The tank system is completely different in Europe than it is in Japan, where they typically use open tanks, but the Q-ton can be used for both (open and closed). It tries to work in a similar fashion to gas water boiler where it can work at low ambient temperatures,” he said.
Yoshida presented case studies from two hot spring inns in Matsumoto and Kanazawa, Japan. At the two locations a hybrid system with boiler was used. The set-up included an imbedded cylinder tank, and a faucet utilising the existing tank and boiler, with the purpose to facilitate bathroom and shower facilities.
Other Q-Ton installations include:
- An office block in Germany utilising three Q-Ton units with closed tank 1000L capacity.
- Hotel retrofits in the UK and Spain, both using two Q-Ton units
- Student accommodation in the UK supplying domestic hot water for 48 students using 6kW immersion element
Heat pumps central to Sanden’s all-CO2 plan
Earlier at the conference Sanden confirmed plans to steer away from HFCs in the coming years and adopt 100% CO2 technology. With new headquarters opening up in Brittany, France, Sylvain Gillaux of Sanden’s European division said the company hoped to boost sales of its heat pump range for household and light commercial, as part of the accelerated transition.
“Wherever we have a need for heating or cooling, we want to meet this need with CO2,” Gillaux explained. “Providing some CO2 modules we want to concentrate on what we do, be it heating, hot water or space heating, and work with the specialists of this market with already strong brand names and use our CO2 modules.”
Sanden’s hat pumps for hot water come in two models: the first with 4kW capacity and a COP of 3.0 for domestic applications; and the second with 6kW capacity and a COP of 3.3 for light commercial needs.
Sanden plans to bring its experience in Japan to Europe with a particular focus on increasing penetration in the commercial sphere.
ATMOsphere Europe 2015 event page
Raniero Trinchieri presentation
Michael Miranda presentation
Shigeru Yoshida presentation