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

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.

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

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)

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

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 %

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

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

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 1960-1990 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

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

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

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

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)

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

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

Heating energy consumption of a residential building:

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

Normalized performance indicator in DH buildings, purchased heating energy Source: 4.11.2015 Energiateollisyys ry

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

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

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.

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

Classification of fuels: Fossil fuels Renewable fuels

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

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

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

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

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) (http://www.hiilipuu.fi/articles/carbon-cycle)

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