Abstract
Abstract This study investigates the performance of an integrated CO2 (R744) heat pump and chiller unit in a Norwegian hotel. The system consists of a single unit for heating, cooling and hot water with an integrated thermal storage. The thermal system of the hotel is described and data from the first year of operation are analyzed. Using the field measurements, hot water loads and COPs are calculated and averaged to 20-minute intervals. The heating and cooling capacities supplied by the R744 unit are studied on a weekly and monthly basis to evaluate the seasonal behavior of the system. The hot water storage holds an energy capacity of 350 kWh at fully charged conditions and demonstrates peak demand reductions of more than 100 kW during a 2-day period. The results show that the hot water usage accounts for 52% of the annual heat load of the hotel. Energy efficiency analysis of the integrated R744 system reveals an annual system SCOP of 2.90, and thus an untapped system potential that can be exploited by increasing the AC load delivered by the R744 unit. Other factors that greatly influence the efficiency of the system are variations in the ambient temperature and high gas cooler exit temperatures. The latter is often a result of high temperatures in the water returning from the subsystems of the hotel. This can be improved by reducing the number of starts and stops of the R744 unit and by insuring stratification in hot water tanks.
Highlights
In order to secure a sustainable future, it is necessary to adopt more efficient means of converting, storing and using thermal energy
The energy efficiency of the system including the provided heating, AC loads and coefficient of performance (COP) are evaluated in the following subsections
This work investigated key operating parameters for an R744 heating and AC cooling unit installed in a Norwegian hotel
Summary
In order to secure a sustainable future, it is necessary to adopt more efficient means of converting, storing and using thermal energy. R744 is firmly established in both heating and refrigeration applications and is accepted as a viable alternative in several sectors, e.g. supermarket, transportation, domestic hot water (DHW) heat pumps and industrial processes (Gullo et al, 2018; Hafner, 2015; Nekså et al, 2010). As illustrated by Cecchinato et al (2005), a suitable R744 heat pump design is imperative to ensure a high efficiency when compared with hydrofluorocarbon (HFC) installations, such as R134a. The design and operation of the secondary system, especially the DHW storage, is important to ensure high efficiency in R744 HPWH installations. Transcritical R744 systems with integrated heating and cooling applications are traditionally found within this sector, where excess heat is recovered as a byproduct of the refrigeration process (Pardiñas et al, 2018; Hafner, 2017; Girotto, 2016). A 6 m3 DHW storage is included in the thermal system for peak load shaving, the operation of which is presented and discussed
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