Discrete demand side control performance under dynamic building simulation: A heat pump application
Highlights
► Discreet Demand Side Control is developed to enhance renewable energy utilisation. ► It is integrated within a detailed dynamic building simulation platform, ESP-r. ► It can quantify the environmental impacts and thermal comfort within the buildings. ► A case of renewable-powered heat pump is used as an example to apply DDSC.
Introduction
Demand Side Management (DSM) applications make use of centralised controllers and two-way metering systems to shift electric loads, switch off appliances and delay itemised consumption. DSM applications using low-carbon electricity sources can bring about economic and environmental benefits in the form of improved demand–supply matching, maintain or improve thermal comfort, reduced operating costs and lower carbon emissions. From the consumer perspective, the combination of DSM control systems alternating grid electricity and intermittent energy from clean/renewable sources can reduce heating bills and improve the service whilst maintaining acceptable levels of comfort.
DSM programs typically work upon the condition that either the demand side can respond to price signals at peak times or other enablers allow load shifts i.e. variations in supply frequency. The inelasticity of the demand curve for electricity suggests that the economic leverage of some of the DSM programs involving active consumer participation is often insufficient to encourage the consumer to shift loads [1]. Discrete Demand Side Control (DDSC) through intelligent algorithms is an alternative to consumer-driven load shifting. In the wide spectrum of DSM programs, including real-time pricing, time-of-use pricing, demand bidding, interruptible programs, and direct load control, these impact on the consumer by making them aware of load management being implemented and therefore a reduction in load functionality or comfort being experienced. The application of this bottom-up approach to demand control using DDSC results in automated load control being implemented so long as the service provision each load is providing is within upper and lower limits of acceptability. This approach offers one solution to integrate intermittent micro-generation systems within the built environment.
This paper reports the use of a detailed building simulation platform to assess the impact of applying Discrete Demand Side Control on a heat pump based space heating system used to supply heating to both a light-weight and a heavy-weight building. The controller tolerance, in terms of time variance of supply, makes it possible to combine a wind turbine as the primary electricity supply with the electrical network. This paper compares the performance of the Discrete Demand Controller in terms of: the match between demand and supply in high tolerance and low tolerance scenarios; its impact upon the built environment as to thermal comfort; the amount of energy utilised from intermittent sources – a wind turbine; and the consequent reductions in operating costs and carbon emissions.
This paper commences by reviewing existing DSM applications making use of demand control systems (Section 2). It explores the issues and challenges associated with energy utilisation from micro-generation systems (Section 3). It introduces a Discrete Demand Side Control algorithm (Section 4) and implements it within dynamic building simulation software (Section 5). The controller is applied to a heat pump system powered by a 6.5 kW wind turbine, with support from the grid; and assessed in high and low tolerance scenarios as to demand/supply match, thermal comfort, and avoided operating costs (Section 6).
Section snippets
Existing DSM applications using demand control systems
Several technological attempts have been made to implement controllers for DSM purposes. This section reviews some recent DSM applications which made use of different typologies of demand control systems.
Moholkar [2] carried out trials on a Computer-Aided Home Energy Management (CAHEM) system which enables the implementation of price-responsive load management for the residential sector. This consists of a computerised load control implemented with the help of X10 appliance controllers, the
Issues and challenges for energy utilisation from micro-generation systems
Concerns over climate change and energy security are driving strong international and national policy action in favour of low-carbon energy solutions. Options attracting support include those using renewable or low-carbon energy resources (such as wind or solar power, and nuclear energy), systems offering high overall efficiency (such as combined heat and power) and approaches to capturing and storing carbon dioxide otherwise emitted from fossil-fuelled energy systems. Some of the technologies
Distributed demand side control (DDSC) algorithm
A detailed flowchart identifying the procedures implemented in the DDSC algorithm is illustrated in Fig. 1. It contains two levels of operation: the first undertakes energy matching between demand and supply at a systems level; and the second establishes the resulting environmental conditions for each individual demand.
At the system level, the algorithm automatically groups selected demands depending on the tolerance level to control being enacted upon them and structures these three clusters:
Implement DDSC within a dynamic building simulation software
The DDSC algorithm, described in the previous section, has been integrated within a detailed building simulation platform, ESP-r, as a new controller. This controller allows a certain tolerance level within the built environment to accommodate time variance of supply from renewable sources. It is able to assess the potential of DSM resources and quantify its impact upon the environmental conditions inside a building. The idea is to utilise the thermal capacitance associated with the building
DDSC analysis through heat pump application
In order to demonstrate that the DDSC algorithm can be run to produce useful results, an application of an electrical powered heat pump system, which works on heating mode to supply heat to the building, is set up. The electricity required for the heat pump can be from either intermittent renewable energy technologies or a conventional electrical supply network. In this analysis, a supply system consisting of a Proven 6.5 kW wind turbine supported by the electrical supply network is used. The
Conclusions
A discrete demand side control (DDSC) algorithm has been developed and integrated within the detailed building simulation platform, ESP-r. This algorithm is capable of simultaneously considering environmental parameters and energy supply variation to control and optimise demand.
A case of a heat pump system powered by a wind turbine with back-up from the electrical supply network to supply heat to a single zone building model during a typical winter period has been set up. Various scenarios
Acknowledgements
The authors would like to thank the UK EPSRC for their support for the research programme “SuperGen Flexnet: Citizens, Customers and Loads”, within which the DDSC algorithm was developed.
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