Energy vs exergy use in buildings
Fraunhofer Institute for Building Physics (IBP)
Department Energy Systems
Christina Sager
Tekn. Dr. Dietrich Schmidt
Auf Wissen bauen
© Fraunhofer IBP
Objectives
Energy savings and reduction of CO2-emissions:
By the use of
low valued and environmentally sustainable energy
sources
for heating and cooling of buildings.
Through utilization of the EXERGY concept
Why exergy?
- Matching of the energy quality of demand and supply
Energy supply
Energy demand
Source
Fossil fuels,
electricity
Low
temp.
District
heating
supply
55
°C
115 0C
Low temp.
Ultra
low
supply
55temp
°C
supply 40 °C
0
Source: VTT
1
Energy quality q
Energy quality q
1
Appliances,
Lighting
Sauna
Domestic hot water
Space heating
0
Approach: Exergy concept
matching the Quantity AND Quality levels of
supply and demand
Quantity  Energy savings
Quality  use of low quality sources
e.g. solar thermal heat,
ground/air heat
Analyses tools for LowEx systems
Software tools for an
energy/exergy assssment
7% exergy
fraction of the
energy
Benchmarking of system solutions
Power primary energy
Non renewable
Cond.
boiler,
radiators.
Biomass,
floor
heat.
GSHP,
floor
heat.
Benchmarking of system solutions
Power primary energy
Non renewable
Renewable
Cond.
boiler,
radiators.
Biomass,
floor
heat.
GSHP,
floor
heat.
Benchmarking of system solutions
energy
Renewable
Non renewable
Biomass,
floor
heat.
GSHP,
floor
heat.
power primary energy /
exergetic fraction
Renewable
Non renewable
Cond.
boiler,
radiators.
exergy fraction
Exergetic fraction of the
primary energy power
Benchmarking of system solutions
Limit
LowEx
ideal
Biomass,
floor
heat.
Cond.
boiler,
radiators.
WP
GSHP,
floor
heat.
Exergy
demand
of zone
Low Exergy Buildings?
Match quality levels of supply and demand
by exploiting low quality, waste or environmental sources
Passive house
Qend = 70
kWh/m2a
Qend = 16
kWh/m2a
QH = 15
kWh/m2a
QH = 60 kWh/m2a
Air heat
recovery unit
...no combustion in buildings
...but LowEx buildings are not Passive House buildings
Source: ETH, Meggers
Low Exergy Buildings?
minimize primary energy:
by exploiting low quality, waste or environmental sources
Passive house
Qend = 16
kWh/m2a
LowEx house
Qend = 6
kWh/m2a
QH = 15
kWh/m2a
QH = 40
QH = 402
kWh/m
a
kWh/m2a
Air heat
recovery
unit
...no combustion and minimum high exergy (primary energy) input
Source: ETH, Meggers
40% solar
fraction
Ground
source
heat
pump
Building systems: Examples
Heat/cold emissioning systems
and storages
Building systems: Example
Ground heat exchanger
(mainly for cooling)
Source WH Zwickau, Germany
 Energy poles
 Bore holes
 Horizontal heat exchanger
 Horizontal heat exchanger
with capillary tubes
Source City of Kassel, Germany
Maximum energy efficiency in buildings
ZUB in Kassel
 Good insulation standard
 Solar-optimized facade
 Effective sun protection
 Thermo Active Building Systems
 Passive cooling
 Demand regulated ventilation
Good comfort
Low energy consumption
© Konstantin Meyer
Thermo Active Building Systems
ZUB in Kassel
Two systems
 Heating and cooling with
concrete core activation or
floorheating system
 Each circle individually
controllable
 Heating with district heating
 Passive cooling via ground slab
© Fraunhofer IBP
Maximum energy efficiency in buildings
ZUB in Kassel
Endenergy: electricity
Endenergy: heating
[kWh/(m²a)]
175
Typical office building
Target value EnBau
70
Consumption
ZUB 2002-2005
39
© Konstantin Meyer
© Fraunhofer IBP
These result have been obtained because of EXERGY thinking
Steady state exergy assessment of buildings
A parameter study
Buildings:
•
2 office buildings
•
Simplification: Office use only
•
Supply systems: district heating and heat pump
•
Heating case only
Method:
•
Building data collected via developed templates
•
Steady state analysis via EBC Annex 49 tool
•
User profiles, climate data, energy demand:
estimated via the German DIN V 18599-10
25. February, 10:00, Tenv.=-4,6°C, No Shading
Building
envelope
Room air
Emission
Distribution
Storage
Generation
Primaryenergy
conversion
Spec. energy/exergy [W/m²]
Energy- und Exergyflows
Building
envelope
Room air
Emission
Distribution
Storage
Generation
Primaryenergy
conversion
Energy- und Exergyflows
District heating (non renewable)
Heat pump (ground coupled)
Concluding remarks
1.
Exergy demands for heating/cooling are very small
- Energy demands are high.
2.
Supply as low exergy as possible to the room space
avoid combustion processes
and minimize electricity input
3.
Find suitable low-exergy sources in the
immediate/local environment.
4.
Development of system-components and their smart
integration are necessary
Why exergy? Therefore:
1.
Exergy is not an “universal” indicator!
But: based on thermodynamics
2.
Gives it differences in building design?
Yes: compared to forced air systems
No: if low temperature hydronic systems considered
3.
Good news:
Not all existing buildings need to be passive houses!
© Konstantin Meyer