Gender Identity Research in Social Sciences: Feminist Voices

Research into supermarket refrigeration systems includes investigation of different topologies and HVAC integration strategies (Cecchinato et al, 2010b; Cecchinato et al, 2012). This field of research also covers secondary loop (SL) refrigeration systems in which the primary system is a vapour compression system and the SL system serves as a distribution system. This type of refrigeration system has also been installed in the supermarket discussed below. Wang et al (2010) reviewed such systems and found that one of the driving forces behind the move towards them was the Montreal Protocol, which enforced the phasing out of chlorinated hydrocarbon refrigerants. Replacement refrigerants may be flammable or toxic, so limiting them to a closely controlled primary system seems advisable. After discussing flammable refrigerants at some length the authors mentioned two R&D challenges. The first one is the degradation of the system’s efficiency due to the introduction of a circulation system including pump(s) and the second is the higher initial costs.

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Tassou et al (2010) published a review on emerging technology for food refrigeration including also a description of refrigeration systems for supermarkets which were considered modern at that time. Such systems used the refrigerant R404A, a multi-compressor pack with an air-cooled condenser and variable head pressure control. The authors found that capacity control for the compressor bank of such systems was achieved by cylinder unloading, on-off cycling of individual compressors and by using a variable speed drive for a trim compressor. This description fits the system analysed below very well, thus it can be concluded that it is representative of a significant percentage of currently installed systems. Therefore results from investigating this system should be not peculiar to this supermarket, but should be valuable for supermarkets in general.

8.1.1 Refrigerated display cabinets

The distinguishing feature of energy consumption in supermarkets compared with other commercial buildings is the influence of refrigerated display cabinets. That is why Hill et al (2014) argued to include the refrigeration system and the impact of these open refrigerated display cases in the NCM, a statutory energy assessment. These researchers found that the NCM severely underpredicted cooling and heating demands which were, in fact, twice as much as lighting for the supermarket used for their case study. However, according to the NCM, lighting seemed to be the largest item in an energy audit. Heating and cooling, on the other hand, were virtually nonexistent according to this methodology.

The effect of indoor relative humidity on the refrigerated display units was examined by Howell et al (1997). These researchers found for the supermarket in Florida they investigated that, if the indoor relative humidity was reduced from 55% to 50%, energy savings of 4.7% were possible for the whole store. Subsequently Bahman et al (2012) built on this work investigating energy saving potentials when assessing refrigeration and HVAC energy consumption together. The methodology developed for researching this supermarket in Florida was based on a moisture balance equation. These researchers discovered that the measured indoor annual average was 51.1% relative humidity, which was below the design value of 55% relative humidity. Their paper reported on the results of reducing the humidity as low as 40%. The authors found that the overall energy used was reduced despite a higher annual energy demand from the air condition system. Kosar et al (2005) investigated reduction of the indoor relative humidity to 35% in supermarkets in general and found that, even then, energy could be saved.

8.1.2 Modelling of supermarket refrigeration systems

Refrigeration systems in supermarkets form a subset of all the commercial vapour-compression systems. Ding (2007) reviewed then recent developments in simulating vapour compression systems. He found that the mathematical models for compressors depended on the aim of the research and divided them into steady state and dynamic models. In conjunction with the steady state models, the author referred to the polytropic exponent, mass flow rate and motor efficiency as necessary model inputs. Evaporator and condenser models were also divided into steady state and dynamic models and, for the latter method, Ding found the following three approaches: lumped parameter models, zone models and distributed models. Regarding the algorithms he observed that the more abstract simultaneous solving method and the sequential module method, which had a more physical meaning, were used. In his review of future developments the author included knowledge transfer into industry and associate problems as well as nanofluids for refrigeration as topics for further research.

The paper reviewing modelling approached by Ding (2007) discussed in the previous paragraph did not include the thesis by James (1976) who researched a produce freezing plant for energy conservation. This researcher used a first principle approach based on the conservation laws to model the steady state and transient behaviour of an air condition system as well as a quick freezing and liquid chilling plants. According to the author his work was particularly useful for improving the control settings of the air conditioning system. He also found ways to improve the capacity control of the freezing plant, but admitted that the model for the chilling plant only offered more insight without yielding definite results.

Ge and Tassou used the energy simulation software package TRNSYS to simulate supermarket refrigeration systems (and whole supermarkets, e.g. Ge and Tassou (2011)).

One example of their work for which these researchers used TRNSYS was the modelling of a multi-compressor refrigeration system (Ge and Tassou, 2000). In the corresponding paper the researchers described the mathematical models in quite some detail taking into consideration points such as the heat transfer between the inlet and outlet of the compressors. The researchers used their model to investigate the benefits of variable speed drives and variable head pressure control. These improvements had become the norm when they published their paper referred to earlier (Tassou et al, 2010).

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When discussing climate change and refrigeration systems, only the effect of the refrigeration system as a contributing cause to climate change is normally examined. One example, is the paper by Wang et al (2010) mentioned above which discussed the need for replacement refrigerants for ozone depleting chlorinated hydrocarbon refrigerants. Another example is Lucas (2006) who explored the consequences for professional practice and changes to life style because of necessary changes in refrigeration technology arising from the need for replacement refrigerants. Earlier examples are summarized in Devotta et al (2005).

The effect of the changing climate on refrigeration systems, however, does not seem to be an area of active research. Therefore the main aim of this chapter is to investigate the impact of climate change on refrigeration systems. A secondary research question revolves around how the condenser fan control could be improved. For this research the supermarket system in Hull was investigated as a typical refrigeration system. A first principle model was chosen for this as such a model allows the investigation of improvement ideas, e.g., in conjunction with the condenser fans more easily then a data-driven model. As mentioned in an earlier chapter, the same type of system has been installed in all the investigated stores. Therefore results of the research here should be relevant to other supermarkets as well.

Figure 8.1: Schematics of a simple vapour compression system

Expansion device

Evaporator

Compressor Condenser with fan