1. Heating and cooling demand in buildings
Martti Veuro
senior lecturer
MAMK
Department of Energy and the Environmental Technology
Building services

2. Buildings are made to have comfortable conditions for humans for living and services in spite of outdoor conditions.
Outdoor conditions are changing all the time → energy and power is needed to maintain the indoor conditions correct.

3. Temperature in January 2011
-34 °C, Mikkeli
Temperature 25th of July 2014
+33 °C, Mikkeli

4. The interest for energy and power consumption of buildings is based on:
energy costs has significantly risen since the first oil crises 1973
fossil energy use increases carbon dioxide emissions to the atmosphere  climate change effect
energy consumption increases continuously in general year by year
20 / 20 / 20 goals by 2020 in EU: 20 % of energy from renewable sources, 20 % better energy performance, 20 % reduction in green house gas emissions (GHGE)

5. In Finland the energy consumption was 386 TWh in 2013
ca. 35 % is domestic and 65 % is imported: security!
buildings account for ca. 40 % of total energy consumption

6. Energy consumption in buildings by energy sources (heating)
district heating 46 %
others 1,1 %
heavy heating oil 1,4 %
electricity 18,6 %
wood fuel 13,1 %
light heating oil 8,2 %
heat pumps 11,6 %

7. At low outdoor temperatures is needed heating power and energy
usually below the outdoor temperature c.a. +10…+15 °C heating is needed (+12 °C in the autumn starts and +10 °C in the spring stops)
between that temperature and indoor temperature +21 °C the internal heat loads and/or solar radiation is enough to provide good conditions indoors
in newest service buildings like offices, shops etc. the internal heat loads can provide enough energy for +21 °C close to +0…+5 °C outdoor temperatures

8. At high outdoor temperatures is needed cooling power and energy
higher indoor temperatures +23…25 °C are usually accepted in the summertime than in the wintertime
cooling / air conditioning is needed not only because of temperature difference (higher outside than inside) but mostly because of internal heat loads and solar radiation
in newest service buildings like offices, shops etc. the internal heat loads may need to be compensated with cooling power starting at close to +0…+5 °C outdoor temperatures

9. Domestic hot water needs heating energy all the year round (total water 100…150 dm³/day, person)
DHW nominal temperature is +55 °C
heat losses of DHW distribution and/or circulation are also internal heat loads in the buildings
in the buildings made in they can be significant (internal heat loads)
in buildings with a separated boiler room and underground pipes for distribution and circulation of HDW (Δt between HDW and ground/soil), significant heat losses

10. Heat flows to the direction of lower temperature
convection (e.g. infiltration / air leakages)
conduction (e.g. building envelope)
radiation, solar radiation through windows into the building

11. Heat flows in buildings in NBC D3 and D5
Qspace = Qconduct + Qthermal bridges+Qleakage air+Qvent.,supply air +Qvent., make-up air
Qint. heat=heatQheat loads
Qheat loads= Qperson+ Qelectricity+ Qsolar+ QHDW, circulation, load+ QHDW, tank/storage, load t
Qthermal bridges
Qupper floor
Qvent=Qheating, vent.
Qvent., make-up air
(mechanical exhaust)
Qvent., supply air (Tsp>or <Troom)
Qleakage air
g –value of window
Qperson
Qsolar
Qelectricity=Wlighting+Wappliances / devices
QHDW, circulation, load
QDoor
QHDW, tank / storage, load

12. Heating: steady state conditions, no solar radiation or internal heat loads are taken into account at the peak power demand
convection (e.g. infiltration / air leakages)
conduction (e.g. building envelope)
radiation, solar radiation through windows into the building, especially during the spring  significant amount of energy

13. convection (e.g. infiltration / air leakages)
Cooling: dynamic process, all indoor and outdoor parameters are changing  cooling power demand is not steady  thermal energy is stored and released to and from the building structures
convection (e.g. infiltration / air leakages)
conduction (e.g. building envelope)
radiation, solar radiation through windows into the building changes according to the time of the day (angle of solar radiation) and the time of the year
internal heat loads
humans
use of electricity (lighting, appliances)

14. Diurnal (daily) temperature variation in Mikkeli airport 19. 8. -20. 8
Lämpötila = temperature
temp. curve

15. Calculations, power (Watts) and energy (kWh)
Heating:
dimensioning power demand in steady state conditions
energy demand monthly method (NBC D5) or dynamic calculations with different time steps, minutes… hours
in energy demand calculations internal and external (sun) heat loads are taken into account, they reduce need of heating energy from the heat source

16. Heating energy consumption of a residential building:

17. Heating energy consumption:
e.g. district heated residential buildings, block of flats: NPI today average 38 kWh/m³,year

18. Normalized performance indicator in DH buildings, purchased heating energy
Source: Energiateollisyys ry

19. Electricity consumption, new trends:
green curve represents the total consumption
the low economical growth explains partly the curve

20. Calculations, power (Watts) and energy (kWh)
Cooling:
dimensioning power demand, dynamic calculations, no steady state conditions
energy demand monthly method (very rough) or dynamic calculations with different time steps, minutes… hours (computer softwares are used)
in cooling energy demand calculations internal and external (sun) heat loads are taken into account
storing of energy to the building structure is in an important part in the calculations

21. The use of thermal energy for heating has decreased:
The use of electricity inside the building envelope has increased continuously so far.
The use of thermal energy for heating has decreased:
better = lower U-values in building elements
tighter buildings
heat recovery of mechanical supply and exhaust ventilation
better insulation of HEVAC-pipes and equipment
more internal heat loads because of electricity usage (all used electricity is converted to heat)
better automation e.g. control of flow water temp.
radiator thermostats etc.

22. The heat production for buildings, heat sources
burning of fuels: either on site or district heating
use of electricity heating, straight /resistance) or in different types of heat pumps
solar collectors (thermal) or photo voltage systems (electricity)
Typical fuels for buildings:
light oil, wood, natural gas, heavy oil
fuels in DH plants: peat, coal, natural gas, wood

23. Classification of fuels: Fossil fuels Renewable fuels

24. Age of fossil fuel: million years Absolutely long cycle
Fossil fuels:
Age of fossil fuel: million years
Absolutely long cycle
Peat: at least thousands of years
Photo: Yle Coal storage in Helsinki
Light fuel oil tank of plastic

25. Age of peat: thousands of years Long cycle
Photo: Turveteollisuusliitto
Peat collection for fuel use

26. Age of renewable fuels: years to hundreds of years
Length of cycle depends on the fuel
Reed canary grass 1-2 years
Willow / Coppice 2…4 years
Wood / trees 15…30…150 years
Pile of energy wood, covered with paper for better drying

27. Renewable fuels:
Green plants are growing by using water, CO2 from atmosphere, nutrients from the soil and solar radiation producing biomass with the help of photosynthesis
Biomass contains C carbon and H hydrogen
Thermal energy can be produced by burning the biomass  thermal energy is used as heat for heating purposes or thermal energy can be converted to electricity in steam-condensate processes in power plants (steam turbines and electricity generators)
in CHP plants both are produced, heat and electricity

28. Producing energy by burning fuels produces carbon dioxide in flue gases:
Burning of fossil fuels is considered to produce green house gases GHG and green house effect
Burning increases the amount of CO2 in the atmosphere, green house gas emissions GHGE
The GHGE are considered to cause the global warming impact on earth
When burning renewable fuels CO2 is released but the next generation works as carbon sink
The next generation captures the released CO2 back to the plants (short rotation) (

29. Emission factors for different fuels
CO2 emission
used in
type
kg CO2 /MWh
DH, large buildings
heavy oil
279
small buildings
light oil
267
DH, buildings
natural gas
202
DH, power plants
peat
382
coal
341
coke
389
wood
(395)
buildings, DH, power plants
electricity
269
average in Finland *1
396
for heating / yearly *2
district heating
217
CHP plants / average *3
161
separated production *4
average in Finland *1 includes all types of electricity production
for heating / yearly *2 use is bigger in cold periods
average in Finland, CHP plants *3
average in Finland, separated production *4