1. Energy performance of buildings
Energy in building

2. Energy performance of buildings
Basic aims of EPB evaluation:
energy need for heating
total energy use
primary energy use
classification of
low-E houses
Energy performance certificate
classification of energy passive houses, EP certificate
Calculation methods:
set of EN ISO (basic EN ISO 13790), national directives…

3. Definitions Energy need for heating [GJ, MWh, kWh/m2]
Heat needed to maintain the required internal design temperature θi
in a space during a certain period (usually a year).
Theoretical value for 100 % efficiency of heating system.
Energy use for heating [GJ, MWh, kWh/m2]
Total amount of energy necessary to cover the energy need for heating QH,nd by means of real heat sources.
It takes into account standardized efficiencies of heat sources, heat distribution and heat emission.

4. Definitions Total energy use [GJ, MWh, kWh/m2] Primary energy
It can be
different from
measured values (many
inputs must be guessed
for the calculation…)
Total amount of energy delivered to a building during a certain period (usually 1 year).
It takes into account standardized efficiences of HVAC and standardized usage of building (e.g. from the point of view of lighting and hot water use).
Primary energy
Energy from nature, which was not transformed in some facility.
Primary energy use [GJ, MWh, kWh/m2]
Amount of primary energy necessary to cover total delivery of energy
to building Quse during certain period (usually 1 year).
It is derived by means of converse factors from Quse according to type of energy
carrier (see following). It show environmental impacts of the building.

5. Energy performance of buildings
Calculation methods:
- (seasonal – over heating period – only exceptionally)
- monthly – present-day standard
- hourly – dynamic simulation programs for complicated buildings
Climate data:
for specific location (for alayses of real energy performance)
reference data (for energy certificate, calculations for various grant programs)
Input data preparation:
definition of zones and their properties (volume, floor area)
areas and properties of constructions (U, g …)
properties of thermal joints
properties of technical systems (HVAC)
selection of appropriate calculation tool

6. Energy need for heating
Energy performance of buildings
Energy need for heating

7. Energy need for heating
Aim of calculation:
classification of buildings:
under 50 kWh/m2: low-energy buildings
under 15 kWh/m2: passive buildings
more subtle limits in TNI and
to get a value without influence of HVAC (grant applications)
Factors taken into account in calculation:
heat losses through constructions and their joints
heat gains (internal + solar)
ability of constructions to accumulate heat
ventilation mode (natural, forced, heat recovery)
intermittent heating and variable usage, if it is acceptable for given
purpose of calculation

8. Energy need for heating
[MWh] or [GJ]
for each month,
annual need =
sum of positive
values
Basic formula from EN ISO 13790:
energy need necessary to cover heat loss of building
the same formulas as for the
calculation of Uem
Exception: heat transfer via the ground, it consists of steady-state and periodic part, various for individual months, calculation according to EN ISO
Approximate calculation:

9. Energy need for heating
Basic formula from EN ISO 13790:
energy need necessary to cover heat loss of building
[MWh] or [GJ]
for calculations: 0,5 / h
ventilation heat transfer coefficient
natural ventilation
forced ventilation (+ heat recovery)

10. Energy need for heating
Basic formula:
energy need necessary to cover heat loss of building
[MWh] or [GJ]
required set-point internal temperature during calculated period
duration of calculated period
mean external air temperature during calculated period

11. generally time-dependent, values, typically in W/m2
Energy need for heating
Basic formula:
[MWh] or [GJ]
Solar gains QH,s:
windows
solar elements (TIM,
Trombe walls, sunspaces)
(opaque constructions) +
Internal gains QH,i:
persons
lighting
appliances
generally time-dependent,
usually taken as mean
values, typically in W/m2
(e.g. family house:
2-6 W/m2)

12. Energy need for heating
Basic formula:
[MWh] or [GJ]
Praha
horizon
Total energy of Sun irradiation during 1 month falling on 1 m2 (depending on orientation)
Solar gains QH,s:
windows
solar elements (TIM,
Trombe walls, sunspaces)
(opaque constructions)

13. Energy need for heating
shading factor for overhangs
shading factor for side fins
shading factor for
other buildings etc.
Basic formula:
[MWh] or [GJ]
default values in EN 13790
effective collecting area (each window separately):
Solar gains QH,s:
windows
solar elements (TIM,
Trombe walls, sunspaces)
(opaque constructions)
window
area
shading reduction factor
reduction factor for moveable shading
frame reduction factor
(ratio of frame area to total window
area)

14. Energy need for heating
Basic formula:
[MWh] or [GJ]
total solar energy transmittance of glazing
effective collecting area (each window separately):
Solární zisky QH,s:
okna
solární prvky (TIM, Trombeho stěny, zimní zahrady)
(neprůsvitné kce)
It expresses total solar energy entering interior:
window
area
shading reduction factor
direct transmission of energy
reflection
reduction factor for moveable shading
secondary radiation
secondary radiation
absorption
declared by producer (for perpendicular radiation), for calculation: 90% from g┴

15. Energy need for heating
Basic formula:
[MWh] or [GJ]
Gain utilization factor:
gains cannot be always
totally utilized
utilization depends on
internal heat capacity C
… and on ratio between
gains and losses
calculation acc. to EN ISO 13790
simplified model
more exactly for hourly method

16. Energy need for heating
Specific energy need for heating:
[kWh/m2]
Total floor area:
only from heated or cooled zones
(without garages etc.!)
includes all floors in heated zones
usually calculated from external dimensions

17. Energy use and primary energy
Energy performance of buildings
Energy use and primary energy

18. Total energy use Aim of calculation:
evaluation of total energy use in building (usually in
kWh/m2)
energy performance certificates
What is taken into account:
efficiencies of HVAC
systems (production,
distribution + emission)
all energy flows in
building
and of course: properties
of constr., th. joints,
gains…
distribution
(pipes)
source
(boiler)
emission
(radiators)

19. Total energy use Basic components of energy balance: [MWh] or [GJ]
energy use for heating
energy use for cooling
energy use for mech. ventilation
energy use for relative humidity adjustment
energy use for hot water preparation
energy use for lighting (event. also for appliances)
Energy uses include also relevant auxiliary energy uses (pumps, ventilators…)
calculation
for each month,
annual use =
sum of monthly
values

20. Total energy use
Annual energy
use:
Monthly energy
uses:

21. Total energy use
Principle of calculation of partial energy use for heating :
heat source efficiency
heat distribution efficiency
heat emission efficiency
auxiliary energy use (pumps, regulation…)
part of energy from solar collectors used for heating
Actually much more complicated!

22. Total energy use
Principle of calculation of partial energy use for cooling:
- at first, energy need for cooling (analogy to heating: gains, losses + utilization)
- further on, all efficiencies and auxiliary energies are taken into account
Principle of calculation of partial energy use for HW preparation:
- starting point: presumed annual (monthly) HW use, starting and final temperature of water
- further on, all efficiencies and auxiliary energies are taken into account
Principle of calculation of partial energy use for lighting:
- starting point: presumed el.power input + light sources efficiencies
- (the same for appliances)
IMPORTANT:
Average energy behaviour of building
is evaluated in monthly method,
therefore all efficiencies are
also mean values!
Principle of calculation of partial energy production:
- starting point: properties of PV panels and cogeneration units

23. Total energy use Specific energy use of the building: [kWh/m2]
Total floor area:
- only from heated or cooled zones
(without garages etc.!)
- includes all floors in heated zones
- usually calculated from external dimensions

24. Non-renewable primary energy
ratio
energy transformation factor
calculation by energy carriers
CO2 emissions:
analogy
emission factor in kg/kWh for individual energy carriers

25. Precision of calculation
dependent on the aim of calculation
for common situations and buildings, the precision of monthly calculation:
is sufficient for annual sum
shows sometimes errors in some months (spring, autumn)
monthly calculation is not sufficient for complicated buildings – dynamic simulations are necessary (ESP-r, TRNSYS etc.)
comparison with the reality:
problematic (how to create the reality model?)
step-by-step calibration of the model can be done

26. Default input values air change rate: natural: n = 0,5 h-1
forced: 25 – 30 m3/(h.prs) [offices 50 m3/(h.prs)]
heat recovery efficiency for ventilation: 75 – 80 %
modern heating system efficiency: 80 – 95 %
internal gains - family and residential houses: ~ 2 – 6 W/m2
gains must be reduced according to presumed building usage
(8 h during 5 days in a week etc.)
the same can be done also for air change rate and required internal design temperature