Determination of the heating efficiency at building level

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Building Physics Ph.D. Seminars 2010

Determination of the heating efficiency at building level

Jeroen Van der Veken

Knowledge Centre for Energy, K.H.Kempen

Prof. Em. Hugo Hens

Laboratory of Building Physics, K.U.Leuven

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Introduction

EPBD i t f th f f

• EPBD ⇒ improvement of the energy performance of buildings throughout EU by taking the most cost-

effective measures

• Calculation procedure to determine the level of primary energy consumption:

– Net energy demand calculated quite detailed and uniform (ISO13790)

– Great variety in accuracy and complexity of calculation gross energy use and total primary energy consumption (efficiency of heat emission, distribution, control and generation)

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Efficiency at system level (EN15316)

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Total efficiency at building level

• Recuperation of losses highly depends on:

– Place – Time

– Building capacity – Building insulation – Solar heat gains – Inhabitant behavior

• Net Heat Demand (NHD) is calculated value – Boundary conditions ?

S t i t ? (i h bit t b h i ) – Set point ? (inhabitant behavior)

• Heating system parts influence each other C t l ffi i ?

– Control efficiency ?

– System efficiency = total efficiency / boiler efficiency ?

Ö D i B ildi E Si l ti P

Ö Dynamic Building Energy Simulation Program

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Simulations : Trnsys 16.1

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Condensing boiler with LT-radiators & room thermostat in well insulated flat

thermostat in well insulated flat

0.9 1.0

0.6 0.7 0.8

cy boiler efficiency

0.3 0.4 0.5

efficienc

system efficiency primary efficiency el.cons. / prim. cons.

0.0 0.1 0.2

jan feb

mrt apr

mei jun jul aug

sep okt

nov dec

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Condensing boiler with LT-radiators & room thermostat : monthly efficiencies

thermostat : monthly efficiencies

0.7 0.8 0.9 1.0

y

K40 K35

0 2 0.3 0.4 0.5 0.6

efficiency

K14 K7 K18 K30

0.0 0.1 0.2

0.0 0.2 0.4 0.6 0.8 1.0

gains/losses

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Condensing or HE-on/off-boiler with LT-radiators

& room thermostat or TRVs

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Overdimensioned boiler with LT-radiators controlled by TRVs

controlled by TRVs

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Overdimensioned boiler with LT-radiators controlled by room thermostat

controlled by room thermostat

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Research by H.Ast & Bach (University of Stuttgart) (University of Stuttgart)

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Research by M.Bauer (UoStuttgart) : emission efficiency including control emission efficiency including control

0 85 0,9 0,95 1

)

Rad light PI Rad heavy PI

0,65 0,7 0,75 0,8 0,85

efficiency (-) Rad heavy PI

Rad heavy TRV Floor light PI Floor heavy PI

0,5 0,55 0,6

0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

A l h ti l d ( )

Floor heavy continu

Annual average heating load (-)

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Influence of emission system and control

boiler correct dimensioned (average insulation)

overdimensioned (passive house) Boiler type Boiler

control

Room control

HTrad LTrad HTrad LTrad

condensing modulating TRV 0.779 0.812 0.696 0.739

condensing modulating onoff 0.751 0.763 0.762 0.769

HE modulating TRV 0.681 0.704 0.602 0.637

HE modulating onoff 0.664 0.668 0.673 0.675

HE onoff TRV 0.404 0.435 0.283 0.310

HE onoff onoff 0 664 0 668 0 664 0 669

HE onoff onoff 0.664 0.668 0.664 0.669

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Influence of variable water temperature

boiler correct dimensioned (average insulated)

overdimensioned (passive house) Boiler type Room

control

Boiler T control

HT LT HT LT

condensing TRV fixed 0.779 0.812 0.696 0.739

floating 0 816 0 833 0 829 0 836

floating 0.816 0.833 0.829 0.836

condensing onoff fixed 0.751 0.763 0.762 0.769

floating 0.762 0.770 0.782 0.779

HE TRV fixed 0.681 0.704 0.602 0.637

floating 0.771 0.722 0.647 0.720

HE ff fi d 0 664 0 668 0 673 0 675

HE onoff fixed 0.664 0.668 0.673 0.675

floating 0.672 0.670 0.690 0.680

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Conclusions

• It is difficult to separate the overall efficiency in production

• It is difficult to separate the overall efficiency in production,

distribution, emission and control efficiency, since the installation parts influence each other strongly.

• These heat efficiencies are not constant; also the building and the inhabitants have an influence on the overall efficiency; with rising heat gains and lower heat losses it becomes more and more g

difficult to control indoor temperatures.

• Ignoring these facts leads to wrong results in the EPRg g g – Overestimation of energy savings

– May lead to wrong choice of heating system-building-inhabitant combination

• The importance of choosing the optimal control and inertia of the heating system will only increase with the current trend of tougher building codes and lowering energy demands

building codes and lowering energy demands.

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Problem : validation radiator model (Jaga Experience Lab)

(Jaga Experience Lab)

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Problem : validation radiator model

simulated dry air temperature is too high simulated dry air temperature is too high

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Problem : validation radiator model water temperatures are OK

water temperatures are OK

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Increased radiator thermal capacity ?

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Increased radiator thermal capacity ?

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h_c,in = 5 instead of h_c,in = 3

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h_c,in = 5 instead of h_c,in = 3

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Problem : validation radiator model

Fl h ti h 3

• Floor heating : h_c,in ≅ 3

• Heavy radiator : h_c,in ≅ 4 C

• Convector : h_c,in ≅ 5

• Jaga DBE (ventilo) : h_c,in ≅ 7

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Problem : radiation ?

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extra losses through backwall : ISSO 1

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Problem : convection

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Emitter tests late 70’s at Liege and Copenhagen

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Stratification is linearly proportional to the power of the convective plume that reaches the ceiling.

Influences:

– Thermal power of emitterp

• Better insulation of the room envelope lowers the nominal power

– Ratio radiation/convection – Location of radiator/convector

• Preferally under window or ventilation opening

– Form of emitter

• Low, undeep, wide radiators show less stratification than high, deep, narrow

di radiators

(Pay attention to window/ventilation)

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CFD calculations by J.A.Myrhen & S.Holmberg based on the older CFD calculations by J.A.Myrhen & S.Holmberg based on the older measurements with air infiltration

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Increased convection coefficients

h_c≈ ΔT h_c ΔT

Heated room ⇒Khalifa

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Measurements in a room with furniture (P. Wallenten)

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Influence of windowsill

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Variable in time : measurements by S.R. Delaforce Wall next radiator Wall next radiator

Ceiling

Floor

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Subzonal models

Ph.D. Peter Riederer

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Subzonal models

Ph.D. Peter Riederer

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Subzonal model

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Alternative for subzonal models ?

Convection at heated wall ≈ power of convective heat

C i ili ifi i f i l h h

Convection at ceiling ≈ stratification ≈ power of convective plume that has reached the ceiling

h _ll≈ Q h_c, wall≈ Q_c

h_c, ceiling≈ Q_c‐ Q_inf h_c, rest ≅ 2

Advantages

• no need for extra zones / variables

• most important hp _c_cvariations over time and place are includedp

¾ influence of wall behind and above emitter can be studied (cfr increased emitter capacity)

¾ influence of increased losses through ceiling can be studied (cfr

¾ influence of increased losses through ceiling can be studied (cfr sleeping rooms and rebound)

Disadvantages

• estimation of Q (validation of JEL measurements)

• estimation of Q_inf (validation of JEL measurements)

• rather unconventional

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Influence on emission efficiency (without control)

Heating system Yearly average heat capacity W/m²

<20 20-40 40-60 >80

Radiator under window

0.97 0.96 0.93 0.9

Radiator internal wall 0.94 0.94 0.93 0.93

Convector under window

0.93 0.93 0.89 0.86

Floor heating 1 1 1 1.05

Ceiling heating 0.96 0.96 0.96 1.01

Air heating 0.91 0.9 0.85 0.83