An international research team has developed a dual-source heat pump (DSHP) heating system that is designed for high water outlet temperature and low ambient temperature applications.
“We have fabricated several prototypes of the dual-source heat pump,” the research's lead author, Jing Li, told pv magazine. “The technology has been applied in some public buildings as well as in a residential house. Then, we also filed patent applications [in] EU, USA, and China.”
The prototype is based on two low-pressure evaporators (LEs), a medium-pressure evaporator (ME), an economizer, a plate-type condenser, a vapor injection compressor, expansion valves, and five air fans. Two of the fans are exhaust air devices and are placed on the top of the DSHP, while the other three fans are discharger air fan devices and are deployed on the bottom.
This system recovers the waste heat from the exhaust air along with absorbing the heat from the outdoor air. Its configuration allows the outdoor air to flow into the outdoor unit and mix with the cooled exhaust air, thus becoming a warmer mixed air, which then flows through the low-pressure evaporators for the second-stage heat exchange. The mixed air releases in turn all the heat energy into the low-pressure refrigerant and becomes colder discharge air than the outdoor ambient.
The vapor injection compressor compresses the evaporated refrigerant from the low-pressure evaporators and mixes it with the medium-pressure refrigerant. The resulting colder refrigerant mixture is then discharged to the plate-type condenser, where the mixture itself releases heat energy to the water.
“Subsequently, a part of the refrigerant flows into the medium-pressure evaporator and economizer for medium-pressure evaporation after corresponding throttling,” the scientists explained, noting that its refrigerant is R410A and the optimum refrigerant charge is 13 kg. “The rest [of the] refrigerant flows through the economizer for subcooling followed by low-pressure evaporation in low-pressure evaporators, finishing a cycle.”
The research group tested the performance of the system on the roof of the central library of the University of Hull, in the United Kingdom, where it was connected to the black exhaust air duct. “The practical DSHP extracts the exhaust air by the duct from the corner window of the office to the top of the DSHP, and then produces hot water and stores it in water tanks by absorbing heat from the exhaust air and outdoor air,” it stated.
The researchers found that the simulated DSHP system was able to provide an average working water outlet temperature of 56.28 C and a stable monthly simulated coefficient of performance (COP) between 2.69 and 3.03 throughout the year. “The simulative heating amount of the DSHP heating system was 9.85% higher than the practical result, while the simulative energy consumption was 6.36% lower than the practical result,” they said, referring to the differences they recorded between the simulated system and the practical one.
Their analysis also showed that, depending on the location, the proposed heat pump system is able to achieve annual heating bill savings ranging from 20.64% to 54.36% and annual carbon reductions spanning from 14.39% to 86.09%, compared to traditional gas boiler heating systems.
The system is presented in the paper “Eco-economic performance and application potential of a novel dual-source heat pump heating system,” published in Energy. The research group comprises academics from the University of Hull and the University of Science and Technology of China.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
I am not an expert but with cold Aircon our roof unit expels warm air from the house so would a heat pump not expel the opposite, cold air? so where are they reclaiming the heat from? Can someone clarify?
Joe, the article says they are pulling hot air through a duct from the office window, and directing it to the heat pump inlet. This then pre-seats the outside air.
Most large building HVAC systems have air ducts out for exchange air, I think they are trying to simulate this.
Most modern hvac systems already have heat recovery units to preheat air inlet air with exhaust air, I don’t know if they are accounting for this in their trials or not.
Like the other commenter said you can simulate this at home by direction exhaust air from you house to the heat pump inlet. Just don’t choke it up with greasy air from a kitchen vent!
Don’t think about this stuff as cold vs hot. Think about calories. To cool an area, you compress a gas into liquid. The compression and then change of phase of the gas requires energy and releases energy, in the form of heat. Calories. These machines make the process, either way, much more efficient either direction, thereby reducing the energy needed to move calories back and forth.
Hot exhaust is a source of calories. Way too simplistic, I know, but just passing info along.
Just locate the building exhaust air behind your air-source heat pump. I did it on my last house, It’s common sense. I can see in larger buildings the value investing in this system when it’s available.
Why waste time experimenting with 410A. It is on its way out.
13kgs of R410a? Geez. Some countries are attaching huge levies to R410a with a view to economical phase out so I’m surprised R454b wasn’t used because this product won’t be around for long with that stuff in it (considering it’s a new product). What’s the nominal output? (13kg: 50kW?)
You could very easily achieve a similar result by venting EA just in front of the ODUs intake side. Does a similar job. Bear in mind the gains are slight. If a commercial office building needs 50kW to heat 500m2 (ish), the exhaust air is likely about 350 l/s (ish) for sufficient ACHs and FA per occupant (ish) whilst the ODU fan would need to pull something like 4,000 l/s (ish).
So if you exhaust air at 20°C and the ambient air is -5°C, it might raise the temperature 2°C or so. Which DOES make a difference to efficiency, but if you look at those COPs they are not that impressive. HOWEVER: most heatpumps start needing to enter defrost cycles at approx 3°C which is kind of an averagely cold UK morning and where heatpumps dip in efficiency – using this feature in this condition you can delay the need for defrost slightly which is how to maximize the feature.
But you can achieve the result by building design rather than a patented product. (By the way, a long time ago I actually studied mech eng at the Uni of Hull myself. I now work as an engineer for a global HVAC manufacturer of heatpumps myself. x)