Impact of standby losses and isotherm blanket contributions on the hot water cylinders of various heating technologies
Authors: Tangwe Stephen Loh , Simon Michael 
Published: October 2018

Purpose
The purpose of this paper is fourfold: to experimentally determine the standby thermal energy losses in various hot water cylinders in both scenarios, without isotherm blanket installation and with isotherm blanket installation; to analytically evaluate the performance of either the geyser, split- or integrated-type ASHP water heaters based on the number of heating up cycles and total electrical energy consumptions over a 24-h period without isotherm blankets and with isotherm blankets installed; to demonstrate the impact of the electrical energy factors of the split- and integrated-type ASHP water heaters under both the scenarios (without and with the isotherm blankets installed); and to use statistical tests (one way ANOVA and multiple comparison procedure tests) to verify whether any significant difference in the standby thermal energy losses occurred for each of the heating devices under both the scenarios.

Design/methodology/approach
The methodology was divided into monitoring of the performance of the electrical energy consumptions and ambient conditions of the hot water heating technologies without isotherm blanket installation and with isotherm blanket installation.

Findings
The results reveal that the average standby thermal energy loss of the geyser without the installation of an isotherm blanket was 2.5 kWh. And this standby loss can be reduced to over 18.5 per cent by just installing a 40-mm thick isotherm blanket on the tank. The statistical tests show a significant mean difference in the group electrical energy consumed to compensate for the standby losses under both scenarios. In contrast, the average standby thermal energy losses for the split- and integrated-type ASHP water heaters were 1.33 kWh and 0.92 kWh, respectively. There was a reduction of 15.5 per cent and 3.5 per cent in the electrical energy consumed in compensating for standby losses for both the split and integrated types, respectively, but there was no significant mean difference in the standby losses under both scenarios for the two systems. Again, without any loss of generality, the electrical energy factor of both the ASHP water heaters decreased upon installation of the isotherm blanks.

Research limitations/implications
The experiments were conducted only for a 150-L geyser and 150-L split- and integrated-type ASHP water heaters. The category of the different types of ASHP water heaters was limited to one because of the cost implication.

Practical implications
The experiments were not conducted with various hot water storage tanks installed in different positions (roof, inside or outside of a building wall, etc.) so that actual real-life observations could be obtained. The challenges of easy disassembling and deployment of systems and DAS to different positions were also a real concern.

Social implications
The findings can help homeowners and ESCO in deciding whether to install isotherm blankets on storage tanks of ASHP water heaters on the basis of the impact of standby losses and its potential viability.

Originality/value
The experimental design and methodology are the first of its kind to be conducted in South Africa. The results and interpretation were obtained from original data collected from a set of experiments conducted. The findings also show that the installation of isotherm blanket on an electric geyser can result in a significant mean reduction in the standby losses. In contrast, an installation of the isotherm blankets on the storage tanks of ASHP water heaters can reduce the standby losses, but there exists no significant mean difference.