Performance Testing of Unitary Split-System Heat Pump with an Energy Recovery Expansion Device

Due to the rising demand of using energy resources more efficiently, the HVAC&R industry is constantly facing the challenge of meeting strict energy consumption requirements. This paper presents a study that focuses on improving the efficiency of a residential split-system vapor compression heat pump using R410A as the refrigerant. R410A, when used as any sub-critical refrigerant in a vapor compression cycle, has a meaningful difference in potential energy savings when using a practically achievable partially isentropic expansion instead of an adiabatic expansion. As a result, there is a significant potential for efficiency improvements by replacing the expansion valve with a work-generating device - an energy recovery expander. The expander functions by using a nozzle to convert enthalpy and pressure of the refrigerant to a high speed flow. The nozzle is designed to ensure refrigerant phase change and accelerate the flow into the impeller of a micro-turbine. The rotating turbine impeller is connected to an internal generator which generates electrical energy. This electrical energy is used in the system to augment the power into the air conditioner’s indoor fan motor. The expander enables the realization of decreased power consumption and increased evaporator cooling capacity. The expander has been implemented into a 5-ton split system heat pump and tested in both heating and cooling modes. The respective heating seasonal performance factor (HSPF) and seasonal energy efficiency ratio (SEER) values have been calculated for the baseline unit and then compared to those with the energy recovery expansion device. The rated values have been experimentally determined based on the standard test procedure regulated by ASHRAE 210/240.The test results will be reported in this paper

Theoretical Analysis of the Impact of an Energy Recovery Expansion Device in a CO2 Refrigeration System

Carbon dioxide (CO2) is being widely used as a refrigerant in HVAR&R applications due to its low Global Warming Potential (GWP). There are many aspects of CO2 systems that make it unique to other traditional refrigerants in that it has higher pressure levels and typically operates at transcritical levels. These higher pressure levels make CO2 systems ideal for installing an energy recovery expansion device that consists of a nozzle, micro-turbine and a generator. The expander functions by using a nozzle to convert the pressure of the refrigerant into a high speed jet that is directed into the impeller of the micro-turbine. The turbine impeller then spins a shaft that is coupled with a generator to generator electrical energy. This energy recovery expansion device is to replace the passive thermostatic expansion valve (TXV). Experimental testing of this device with R410A indicates that the device is more suitable for systems of higher pressure levels and with lower density refrigerants. For these reasons, the implementation of this energy recovery device in a CO2 refrigeration system for marine transportation has been investigated. The results of this paper quantifies the potential impact that this device could have in the system in terms of theoretical recoverable power. This recovered power has then been used to understand the impact on other various system parameters like COP, SEER and HSPF. This paper aims to present whether or not pursuing further experimental research on installing this energy recovery device into a CO2 system is of interest.

Performance of Finned Heat Exchangers after Air-side Foulingand Cleaning

Air-side fouling of enhanced surface heat exchangers by particulate matter may significantly reduce their performance. Hence, the effect of particulate fouling and subsequent cleaning on the performance of finned heat exchangers is investigated. It is anticipated that heat exchanger geometry and operating conditions such as air velocity, air humidity, and concentration of dust in air will impact the process of fouling and subsequent performance degradation of heat exchangers. In the experimental phase of research, heat exchangers being tested are installed in a wind tunnel where all air-side parameters can be controlled. ASHRAE standard test dust is injected into the air stream in a controlled manner leading to fouling of the heat exchanger. The mass of dust deposition on the heat exchanger is indirectly measured to quantify the extent of fouling of the heat exchanger. In addition, the pressure drop across and heat transfer through the heat exchanger are also measured to quantitatively evaluate degradation in performance due to fouling. A small set of in-situ cleaning strategies are attempted coupled with a standard detergent-based cleaning procedure to evaluate their efficacy. In the modelling phase of research, a mathematical model is developed to predict the deposition rate and distribution of dust as a function of time using heat exchanger geometry and operating conditions as inputs. Published and measured experimental data are compared against model predictions. To improve prediction accuracy and fidelity of the model with experiments, fundamental measurements are necessary to acquire knowledge of the interaction parameters between the heat exchanger surface and the fouling agent. When this information is lacking, the use of estimated values or tuning factors becomes necessary. It is proposed to extend the developed fouling model to predict the performance of fouled heat exchangers. The predicted fouled heat exchanger performance will then be used to estimate degradation in system performance due to fouling. With this project, it is envisioned to predict the extent of fouling of fielded heat exchangers, and set target cleaning schedules based on the maximum degradation in performance of the heat exchanger that can be tolerated by the system in which the heat exchanger is installed. A comparison of prior-fouling and post-cleaning performances will enable an understanding of the efficacy of cleaning procedures. The experimental procedure developed as part of this research is proposed as a robust and repeatable test protocol for simulating heat exchanger fouling in laboratory conditions