M. Embaye1, R. K. AL-Dadah1, S. Mahmoud1, A. Elsayed1

School of Mechanical EngineeringUniversity Of Birmingham

Birmingham, United Kingdom, B15-2TT

EFFECT OF FLOW PULSATION ON ENERGY CONSUMPTION OF A RADIATOR

IN A CENTRALLY HEATED BUILDING

SusTEM Special Sessions on

Thermal Energy Management

PRESENTATION OUTLINE

1. INTRODUCTION2. MATHEMATICAL MODELLING 3. MATLAB/SIMULINK MODELLING 4. OPEN LOOP SYSTEM 5. CLOSED LOOP SYSTEM6. CONCLUSIONS

�The European Union is demanding for a reduction of energy consumption by 20% before 2020.

�Optimization and reducing of energy consumption for residential buildings is a vital issue in the context of global warming effect.

�To fulfil this protocol the UK has targeted to decrease its total energy consumption for residential buildings by 52%.

�The essential step to achieve this target is to enhance the thermal performance of the central heating system.

�Enhancing the thermal performance of central heating system in buildings can play a major role in the energy saving strategy adopted by the UK.

1. INTRODUCTION

� Convective panel radiators work well with all heat sources only need hot water supply.

The central heating appliance and the heat source

Schematic diagram of hydronic central heating system

1.1 Work done/literature review for enhancement of the thermal performance of the heater radiator

� Convection heat transfer output through panel radiator can be improved by increasing air flow on its heat transferring surfaces

� Coating the wall behind the radiator with high emissivity material results high heat output of the panel radiator

� Placing one or two high emissivity metal sheets between the interior surfaces of double panel radiators can enhance the heat output of the heating system.

� Correct position of the radiator inside the room ( bellow the outside window) also improve the heating balance as a result improve comfort of the occupants

� The control strategy used in any domestic central heating system can play a major role in improving its energy consumption and carbon emissions

1.3 Aim of this work

� This work is aimed to improve the performance of the hydronic central heating system by changing the flow strategy from steady flow to pulsed flow

� Without changing the current installed hydronicheater and

� developing a control strategy that can achieve energy saving without compromising the user comfort

� The work carried out involves mathematical modelling and simulation of various operating flow conditions using MataLab/Simulink software

2. MATHEMATICAL MODELLING

� Conservation of energy principle is applied for the heated space including

� The heat supplied to the room from the radiator

� the heat losses to the surrounding due to building structure through the roofs, walls, window, and floor.

The schematic of building with heating radiator

� Conservation of energy was used as governing equation

� Heat output of the radiator to the room

� Heat loss through the building structures:

� Energy balance equation for the centrally heated room/building:

� The dynamic temperature distribution of the radiator:

1. TAUQ radradrad ∆=&

)).(...( ambindflrflrrfrfwallwallwinwinloss TTAUAUAUAUQ −+++=

)]()([)(

21tTAUtTAU

dt

tdTVc BBradrad

indairairair ∆−∆= ∑ρ

2.1.Governing equations

dtTTcV

AUTT

cV

cmT

nt

t

ambind

airairair

tottotoutletinlet

airairair

wind ])(

.)(

.[

0

∫ −−−=ρρ

&

3. MATLAB/SIMULINK MODELLING

� A single room integrated with hydronic heating panel radiator was modelled using MatLab/Simulink

� Simulink is a MatLab graphics user interface, which is used for dynamic system simulations

3.1 Assumptions� The temperature difference in the room is assumed

to be even everywhere in side room � The room is assumed to be empty � The only heat source/gain is from the installed

hydronic radiator � The only heat loss is due the building structure

Matlab/Simulink flow diagram of single room thermal model at various flow input conditions.

Components Materials K [W/m.K] c [J/kg.K] U[W/m^2.K]

ρρρρ

[kg/m^3]UA [w/K]

Internal wall Plasterboard 0.16 840 0.35 950 11.3

External wall Brick 0.77 800 0.86 1700 3.69

Window Glass 0.96 750 1.4-3.1 2400 5.20Floor Screed 0.41 840 0.35 1200 4.03Ceiling Wood wool

slab0.10 1000 0.3 500 3.45

Radiator Aluminium 205 900 7 2700 7

Roomenvelope

Air 0.025 1005 - 1.2 -

Door wood 0.14 1200 - 650 -working fluid Water - 4180 - 1000 -

Trad inlet [⁰C] Trad

outlet[⁰C]

Tamb [⁰C] (average) mass flowrate[kg/s]

Type of controller Tset point [⁰C]

75 65 5 0.01 PID(on/off) 20

3.2.The thermal properties of buildings materials and heater radiator used for this work

�The standard heater radiator operating input values.

� The operating conditions of the radiator inlet and outlet temperature were taken from:� Standard experimental

radiator heating BS EN 442-2 radiators and convectors Part 2(75⁰C/65⁰C)

� The UK winter season temperature was taken as ambient temperature (average of 5⁰C)

� The Comfort indoor temperature of 20[⁰C]

3.3 Operating input value and standards

4. OPEN LOOP SYSTEM SIMULINK ROOM MODEL

�When a system is operating in an open loop scenario:

� In this work the radiator inlet mass flow rate was regarded as the controller

� The room temperature is the controlled variable (output)

Simulink block diagram for Open loop model of the heated room

4.1 Operating hot water flow strategy

�All strategy were operating at average mass flow input value of 0.011[kg/s]

�All pulsed flow were applied below the human threshold of hearing which ranges from 40 Hz to 3 kHz(1.4 Hz utilized in the current analysis).

� All flow input strategies have managed to achieve the 20°C comfort temperature target; but at different time intervals.

4.2Temperature time responses for the open loop case of the various flow strategies

� Steady flow reached the comfort temperature of 20°C at 3800 [Sec]

� Sinusoidal flow reached the comfort temperature of 20°C at 3300 [Sec]

� On/Off flow reached the comfort temperature of 20°C at 3000 [Sec]

� The time difference in reaching the desired temperature indicates energy saving

4.3 Energy saved and consumed to reach the comfort temperature of 20 [⁰C] for each flow

strategies

� Less energy was consumed by using pulsed (on/off) flow strategy to reach the comfort level temperature comparing to the other strategies

� Short response time of the temperature of the room

� About 20% of energy can be saved using flow pulsation

5. CLOSED LOOP SYSTEM

� The advantages of the closed loop system over the open loop system are:

� Improving the dynamical response of the system

� Better accuracy � less sensitivity to

disturbance, noise, and environment

5.1 Temperature time response for the closed loop model �Steady flow reached the

comfort temperature of 20°C at 3700 [Sec]

�Sinusoidal flow reached the comfort temperature of 20°C at 3150 [Sec]

�On/Off flow reached the comfort temperature of 20°C at 2800 [Sec]

� Results shown that the response time of the closed loop for all flow strategies are faster than the open loop case which highlights the potential of using feedback controls in this application.

5.2 Energy saved and consumed for the closed loop case to reach the comfort temperature

�Highest energy consumption occurred in the steady flow case

�Lowest energy consumption occurred in the pulsed flow (on/off)

�About 22% of energy can be saved in the pulsed flow strategy comparing to the steady flow case

�All results obtained from the closed loop case are in a good agreement with open loop case.

6. CONCLUSIONS

�MatLab/Simulink model was developed to investigate heat transfer enhancement by changing the steady flow to pulsed flow for hydronic central heating system

�About 20% of energy can be saved by changing the flow strategy from steady to pulsed flow

�Temperature time response can be shortened from 3800[Sec] to 3000[sec](open loop)

�Both temperature time response and energy saving can be improved by applying control feedback system (closed loop)

&