Conference Agenda

A variable speed residential air source heat pump system generally operates with a variable speed compressor controlled by a fully variable speed drive. This type of system has the capability to operate the compressor over a wide speed range (from very low speed to over-speed) commanded by the algorithm from a system controller. To achieve this wide range of operation, the electronics components must be rated to reach the maximum output power (over 7kW for a 5 ton system). Additionally, the drive is permanently conditioning line power to energize the compressor, constantly incurring losses in the power electronics.

A novel partial variable speed compressor drive is presented that overcomes the abovementioned shortcomings (high power rating, electronics losses) of existing fully variable speed solutions, taking into account that typical HVAC systems would operate above 90˚F ambient for approximately only 7% of the time. With the proposed solution, the system would operate with line power at ambient temperatures higher than 90˚F (AHRI 210/240-2023, Table 13),. Unlike fully variable speed compressors driven with brushless DC (BLDC) motors, the solution uses a regular single speed rotary type compressor driven by an induction (Permanent Split Capacitor, PSC) motor. A lower power rated (2.5kW for a 5T system), output optimized, variable speed compressor drive is used to control the compressor.

The performance of this new solution is validated via psychrometric room testing following the AHRI 210/240-2023 standard. A single speed two-stage PSC rotary compressor is selected to operate with the partial variable speed drive in this system. Two scenarios are tested including variable speed modulation of the compressor speed as a single-stage (high displacement) and as a two stage (high and low displacement). The results show that the air source heat pump system could achieve up to 5 points of SEER₂ rating improvement with the addition of this low power drive to the standard single stage rotary compressor, without redesigning the heat exchangers or outdoor cabinet. Finally, potential benefits of operating the compressor at low displacement stage with the proposed drive are discussed.

The European building sector represents approximately 40% of total energy consumption and contributes significantly with the 36% of the overall greenhouse gas emissions. A primary goal of the European Commission involves the identification of technological remedies aimed at reducing energy consumption and mitigating greenhouse gas emissions. Among these solutions, ground source heat pumps (GSHPs) emerge as a promising avenue, displaying potential for notable reductions in greenhouse gas emissions within HVAC systems. Within the EU GEO4CIVHIC research project, two GSHPs have been designed and installed in a pilot building. The two heat pumps work with R454B (GWP=466) and isobutane (R600a, GWP=3), respectively. R454B is a mid-term mildly flammable refrigerant with a GWP of 466, while R600a is natural highly flammable refrigerant with a GWP of 3. Both the systems are fully equipped with research-kind measurement instruments. In particular, the inlet and the outlet of each component of the refrigerant circuits is equipped with temperature and pressure sensors. On the ground-water circuit and the user-water circuit, temperature sensors are installed at the inlet and the outlet of each heat exchanger, along with electromagnetic flow-meters to measure the water volumetric flow rate. The two heat pumps have been operated in alternate days, in order to be monitored under similar boundary conditions, allowing a comparison of the performance between the two refrigerants. This work describes the monitoring system and presents the first results obtained from the two systems. The comparison is based on the COP values of the heat pumps. Moreover, this work highlights the importance of the refrigerant choice in the system design, and its influence on the cycle components.

As the low GWP refrigerants are widely adopted in HVAC&R and heat pumps, the effects of refrigerant drop-in on the system performance need to be evaluated for the system modification and component redesign. Due to the difference in the thermodynamic properties, the low GWP refrigerant drop-in can change system compacity and COP; as a result, the system operation might require necessary adjustment for optimum performance.

In this work, the refrigerant drop-in from R410 to R32 in a heat pump system has been tested according to the standard EU 14825. The system is a refrigerant to water-ethylene glycol (WEG) system using a variable speed scroll compressor, and its designed capacity is 9 KW. Seasonal performance was evaluated under different test conditions, - the combinations of variable condenser secondary fluid outlet temperature () at different part load with fixed evaporator secondary fluid inlet temperature (), to be specific, the test conditions were: Case 1 (= 35-24°C and = 10°C), Case 2 (= 55-30°C and = 10°C) and Case 3 (= 35-24°C and = 0°C). Maintaining the same compressor frequencies resulted in higher heating capacity with R32 during higher part load conditions (100%, 88%, and 54%); however, higher compressor power consumed with R32, and the calculated seasonal coefficient of performance (SCOP) was 2% lower than R410A with test case 1. Though similar heating capacity resulted for R32 with lower compressor power, SCOP remained the same as R410A because of higher cycling loss at the lowest part load (15%) during test case 1. Compared to test case 1, the SCOP with R32 during test cases 2 and 3 dropped by 35% and 27%, respectively. Additionally, during test cases 2 and 3, the compressor operating conditions suffered from elevated temperature lift and higher pressure ratio. This study can provide a good understanding of refrigerant drop-in effects on the heat pump system performance, which may lead to the modification of the system design.

Heat pump is an alternative technology to the traditional thermal heating process, which can significantly reduce carbon emissions and serve as an effective approach towards industrial electrification. To improve the heat supply consistency and reduce the start-stop losses, in a lot of applications, the heat pump system must continuously modulate the capacity to meet fluctuating heating loads. The primary method of capacity control is to alter the cycle's refrigerant flow rate, which can be done either within or outside the compressor. In this study, the effects of different compressor capacity modulations have been evaluated experimentally. The seasonal performance of R32-water-ethylene glycol (WEG) heat pump system (heating capacity of 7 kW) was tested according to the standard EU 14825. Three different compressor arrangements - single speed, variable speed, and uneven tandem from the same manufacturer, were adapted. By varying condenser secondary fluid outlet temperature (35, 34, 30, 27, and 24°C) with fixed evaporator secondary fluid inlet temperature(0°C), the system can achieve 100%, 88%, 54%, 34%, and 15% of part load conditions, and the effects on the heat pump's seasonal performance have been compared. The results showed that: the system with variable speed compressor performed better than both uneven tandem and single speed arrangements. The seasonal coefficient of performance (SCOP) of a single variable speed compressor was 24% greater than that of a single speed compressor, and it was only 8% and 3% higher than that of uneven tandem modulation with a lower and higher capacity compressor, respectively. In addition, the variable speed compressor’s isentropic efficiency under full load condition was 39% and 16% greater than that of an uneven tandem and a single speed compressor, respectively, under comparable capacity and test conditions. This work can provide insight into the heat pump system component design and performance optimization.

Variable refrigerant flow air conditioners (VRF) are composed of multiple evaporators connected to a single condensing unit, being able to provide thermal comfort to multiple indoor units simultaneously but using a compact arrangement. VRF air conditioners may operate with constant or variable speed compressors, and electronic expansion valves, which allow fine tune of the cooling capacity in each of the indoor units at high efficient operation. As a result, VRF systems have been increasingly adopted in household and commercial applications as an alternative to conventional split type or ducted air conditioners. Although these systems are in evidence in the literature, there is still room for experimental researches approaching detailed analyses of the thermal load on the air conditioner performance. This paper presents a parametric analysis of a VRF air conditioner with two evaporators (VRF2E). An experimental facility was built for this purpose and a commercial VRF2E was instrumented with temperature, pressure and power sensors. The experiments were conducted according to a two-level factorial design which had four independent variables: (1) the total thermal load handled by the VRF; (2) the proportion of the total thermal load handled by each evaporator; (3) the set-point temperature for one of the evaporators and; (4) the air temperature in the outdoor unit. The dependent variables were the mean compressor input power, the VRF2E coefficient of performance (COP) and the temperature and relative humidity of the return air in the indoor units. It was found that the total thermal load change does not imply in a variation of the COP. However, an uneven distribution of loads between the indoor units reduces the COP, indicating that it is preferable that both indoor units share similar amount of thermal load to maximize the COP.