The performance gap; verschil tussen berekend

en werkelijk energieverbruik-de schil-

POST DOCTORAAL ONDERZOEKER

Universteit Gent (UGent)

Marc Delghust

PROBLEM STATEMENT

context: energy performance assessment

~200 000 cases EPC label database Netherlands 2010

[Majcen, 2016]

calculated

real

old housing neighbourhood current standard housing neighbourhood

old vs. new

old vs. new: space heating

[kWh/(m².year)]

old vs. new: space heating

theoretical gain

real gain ?

[kWh/(m².year)]

Blame it on the user?

…or on the building?

…or on the modeller?

…or on the model

?

• Technical default values

• Heating profile: master bedroom?

• Ventilation profile: standard vs. real, total and at room level

REAL CHARACTERISTICS OF A BUILDING

(optional) conservative simplifications

Vinf = 0.04 * v50 * Sloss– large, detached houses => Sloss ↗

– low energy demand => % ↗

% d

iffe

ren

ce

en

erg

y d

em

an

d

real –

pre

dic

ted

( )( )

• Envelope– Default values

• Air permeability v50• Thermal conductivity λ• Solar shading angles• …

– Formulas & methods• Thermal bridges (A/B/C)• Ground heat losses (P, A)• …

• Systems• Return temperature & efficiency• Ventilation rate with vs. without system• …

(optional) conservative simplifications

∑

x

( )

( )(optional) conservative simplifications

∑

x

• Envelope– Default values

• Air permeability v50• Thermal conductivity λ• Solar shading angles• …

– Formulas & methods• Thermal bridges (A/B/C)• Ground heat losses (P, A)• …

• Systems• Return temperature & efficiency• Ventilation rate with vs. without system• …

MEASUREMENTS

Envelope: IR thermography

• Relative indication, spotting weak spots

• …

Envelope part: heat-flux measurements

(An-Heleen Deconinck)

=

=

−

=n

j

sij

sej

n

j

sij

M

q

R

1

)

1

(

ISO 9869:1994(E)

Envelope part: heat-flux measurements

(An-Heleen Deconinck)

Whole envelope: co-heating tests

(Geert Bauwens 2015, 2019)

Things to consider…

• Measurement uncertainties

• Still requires models (for data analysis), with simplifications & uncertainties

• Interpretation or lack of it – Still requires expertise (results & their meaning)

• Open window vs. hole in the wall?

• Normalisation and attribution challenges: climate & user

• The house has to be built first, thus for post-evaluation…

• Delay (used (changing?), dry, commissioning …)

• Monitoring hardware challenges

• …what do we (need to) evaluate?

REAL USE OF A BUILDING

Heating profiles

(VEA REG -enquete, 2008)

96

90

20

67

26

4

10

79

32

68

0 20 40 60 80 100

eet- en zitkamer

keuken

slaapkamer(s)

badkamer(s)

hal

%

Ja Neen

Q25: Welke ruimtes worden er overdag verwarmd als er iemand thuis is?

Niet het vorstvrij houden van verwarming. (basis: allen)

Predicted savings

• Roof insulation

• Double glazing

• Cavity wall ins.

• Floor insulation

Predicted savings

• Loft insulation

• Double glazing

• Cavity wall ins.

• Floor insulation

Single-zone vs. multi-zone

SAVINGSAVERAGE TEMPERATURE

°C

SAVINGS

• Loft insulation

• Double glazing

• Cavity wall ins.

• Floor insulation

single-zone bias

overestimated

savings

underestimated

savings

Predicted savings

Potential for optimization

?

• What’s best for (individual) comfort?

• What’s optimal (comfort+energy+IAQ)?

Simplified: single-zone

(EPB, eco-design)

More accurate: multi-zone

(heated vs. unheated)

(Janssens et al. 2018)

Also systems, e.g. ventilation

Internal zoning & ventilation

(Janssens et al. 2018)

multi-zone system?

Neighbours…

-2°C

= you normally save approx. 20%

inner flat -2°C

= you save approx. 35-71%

= your neighbours spend 10-20% more[source: Nielsen & Rose 2014]

EPB 2018: K-peil => S-peil, one of the changes:

also heat losses through common walls/floors

• Use common sense• Using simplified calculation methods? => know and consider the

simplifications and limitations

• Be coherent (e.g. don’t mix tools and assumptions, e.g. EPC vs EPB vsdyn.sim. vs measured …)

• Consider the different zones inside the ‘envelope’ => differentiation (design & control)

• Make zonal differentiation possible, whether for smart buildings or for smart users• For

• energy efficient

• personal(!) comfort

• health (e.g. IAQ)

• By

• Internal zoning (making choosing possible): construction & systems

• (facades) controls (with overrides)

Things to consider when evaluating and optimizing…

dr. ir.-arch. Marc DelghustUGent – Faculty of Engineering & ArchitectureResearch group on building physics, construction and services

marc.delghust@ugent.be