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Dynamic demand side management of heat pump integrated with thermal energy storage

Christopher Wilson Loughborough University – 29th June 2015

Introduction

Project Title

• Dynamic demand side management of heat pump integrated with thermal

energy storage

Scope of the project – Aims and Objectives Methodology Analysis Results and Outputs Summary

Thermal Storage DSM Heat Demand Heat Pump

Direct Heat Indirect Heat

Project Scope

RETROFIT

• Radiators +60°C
• Minimal Disruption
• Suitable for existing trade

workforce

• Retrofit – “plug & play”
• Max 80°C flow temp
• Seasonal COP – min 2.5 to

be renewable – what is the max achievable?

• Thermal comfort – gas
• Electrical for DSM.
• Cost effective over life

cycle.

Thermal Storage

Thermal Storage DSM Heat Demand Heat Pump

Direct Heat Indirect Heat

Sensible heat storage

• 600 litre buffer tank
• 14 kWh useful – delta-T 20 (55-75°C)
• Energy loss - 1°C/hr
• Lower heat pump heating coil
• Upper house central heating coil
• Cylinder stat
• Temperature monitoring
• De-stratification pump
• Needs to be high capacity – low energy loss
• Compact for domestic situation
• Meaningful thermal store over 24 hours to

realise DSM capabilities Other energy storage options…

• Latent – PCMs
• Thermochemical
• Increased storage capacity
• Reduced storage volume

DSM

Thermal Storage DSM Heat Demand Heat Pump

Direct Heat Indirect Heat

Electric Tariffs Wind Penetration

Daily electricity price variation

• Peak around 15:30 – 19.30
• Price not lowest at night –

some flexibility

Wind production forecasting…

• Managing wind energy variability
• Ability to flexibly control DSM tools

to balance the grid Wind farm dispatch down across Ireland – 2012

• Instead of turning of wind farms – Turn on

heat pumps

• Energy potential utilised
• Increased wind energy penetration

Methodology

Retrofit:

• Bypass existing gas boiler
• Remains in place as backup
• Uses existing heating controls

2 scenarios with heat pump:

• 1. Heat house directly
• 2. Heat house indirectly via

buffer and storage tank

House heated via buffer tank

• More heat delivered from heat

pump than delivered too house

• Heat pump is on reheat mode –

maintains buffer at 75°C

• Daily heat loss of 20 kWh in some

cases – 82% efficiency

Benefit of buffer tank

• High instant power
• House thermostat quickly

satisfied

• Heat pump running long

durations – benefit might not be justified.

Dynamic DSM Controller via Raspberry Pi

Raspberry Pi

• Credit card sized low cost computer - £30
• Enables physical computing – ability to control relays +

measure sensor inputs (buffer tank temperature)

• Write python software to control input and output pins
• Connected to network – retrieves internet data and network

control – real time forecast demand

• Email alerts to phone for malfunction and switches off

leaving heat pump in default direct heating mode

Dynamic DSM Controller via Raspberry Pi

Normal Operation – Direct Heat

• House call for heat
• Relay A normally

closed

• 3PV energises –

direct heating

• Relay B energises –

HP on Rpi Control – Charging

• Benefit to store
• Buffer tank less

than 75°C

• RPi Pin 12 closes
• Relay C energises –

HP on Rpi Control – Using stored heat

• Benefit to use
• Buffer tank > 55°C
• RPi Pin 11 closes
• Relay A energises –

Heating pump on

Results & Further Work

Initial testing:

• 1. Raspberry Pi control - dynamic switching between direct and storage mode
• Only recently installed – further analysis required – tweaking of input

parameters

• Testing using forecast wind electricity production
• Testing using real time electricity pricing
• Formulation of optimised demand side management method – Renewable

Electricity Tariff

• Machine learning techniques for true plug and play “dsm adaptor”
• Specifications of HP and thermal stores required for efficient DSM

Summary

The project goals…

• Heat pumps to meet the energy demand of domestic house
• Retrofit system and integration
• Thermal storage – improve heat pump integration
• Thermal storage – DSM role
• Demand side management control
• COP of HP needs to improve
• Thermal store needs to increase capacity/reduce in size
• DSM control needs further optimisation to justify its use and

incentivisation

Thanks for your attention. Any Questions?