Heating energy calculation methods

Anti HamburgLecture TTK-UAS

1. Heating energy consumption2. Electricity consumption3. Cooling energy consumption4. Hot tap water boilers energy consumption

Basics about energy consumption 1

Basics about energy consumption 2

Energy efficiency regulations in EU countries

Compareing consumption:1. Primary energy2. Final energy3. Overall Net energy demand limit4. Heating energy 5. Heating and cooling energy

Differences

Basics for heating energy calculations

• Envelope elements and materials• Materials thermal conductivity• Envelope areas• Way of managing ventilation and airflow rate

Heat lossesH BE = ΣU i A ⋅ i+ ΣΨi l⋅ i

U i – Envelope thermal conductivity, W/m2 K⋅

A i– Envelope area, m2

ΣΨi – thermal bridge conductivity, W/m K⋅

li – thermal bridge lenght, m

H vent= ΣL c ρ (1- f)⋅ ⋅ ⋅

ΣL– air change, m3/sC – air specific heat, 1005 J/kg K⋅ρ – air density, 1,2 kg/m3

f – heat recovery efficiencyH infilt= qi c ρ⋅ ⋅

qi – air change, m3/s

Heating energy consumption calculating methods

1. Degree-days method (static method to analys annual energy use)

Degree-day for heating period

• Weather data for heating energy calculations • In every region have own and also different

weather data• Degree-day shows how long period we should

heat our houses• Degree-day are used with balanced

temperature

Different climate every region

Illustrative picture

Balanced temperature and degree- day

• Balanced temperature is temperature where we have take away temperature increase from free heat

• Free heat temperature increase means mainly heat from people, electrical devices, lighting and free heat from sun

• If we can get lot of free heat on heating season then we have low balanced temperature

Balanced temperature

Balanced temperature

Free heat

Real need for heating

Room temperature

Calculated heating power

Outside temperature

Balanced point

Out

side

tem

pera

ture

Days

Need for cooling

Balanced temperature and heat losses

• Free heat temperature increase big when we have heatlosses through envelope and ventilation ΔtFH=ΦFH/H

• Calculateing balanced temperature is also important to know how big is or sould be indoor air temperature tB=tIN-ΔtFH

Balanced temperature and degree-day

• One degree day represents 1 ° C temperature difference between the estimated 24-hour period average internal ambient air temperature.

Estonian degree-daysTB SUM

Heating energy consumptionQ HL = H S 24 10⋅ ⋅ ⋅ -3

Q HL – Heating energy useage, kWh/a

H – Building specific heat conductivity, W/KS – Degree-days, °C d⋅24 – day, hH= H BE+ H vent + H infilt

H BE – Building envelopes

H vent – Ventilation

H infilt – Infiltration

Heating energy consumption calculating methods

2. Monthly average ambient outdoor temperature method (were used befor degree-days method)

Calculated enery usageHeating energy use per heating surface Degree days 3974°C/d

Balanced temperature=16.25 °C

Envilope Area m2 Estimated U‑value, W/(m2K)

Estimated heat loss kWh/a Percentage

Insulated exterior wall 739.46 0.26 18337

12.3Original exterior wall 867.00 0.26 21500

Roof 762.96 0.26 18920 5.9

Floor 762.96 0.25 18192 5.6

New windows 468.2 1.60 71448 22.1

Windows 17.02 1.60 25971.2

Exterior doors 8.36 1.60 1276

Volume m³ Air exchange rate Estimated heat loss kWh/a

Air exchange 8910 0.6 170810 52.9

Σ 323079

Heating energy use per heating surface 97.9 kWh/m2*a

Heating energy consumption calculating methods

3. Dynamic simulations (can be taken out of the current energy use is also best but difficult calculation method)

Programs based on ISO 13790:2008 standard

ISO 13790:2008 standardISO 13790:2008 gives calculation methods for assessment of the

annual energy use for space heating and cooling of a residential or a non-residential building, or a part of it, referred to as “the building”.

This method includes the calculation of:• the heat transfer by transmission and ventilation of the building

zone when heated or cooled to constant internal temperature;• the contribution of internal and solar heat gains to the building

heat balance;• the annual energy needs for heating and cooling, to maintain the

specified set-point temperatures in the building – latent heat not included;

• the annual energy use for heating and cooling of the building, using input from the relevant system standards referred to in ISO 13790:2008 and specified in Annex A.

Example

Heating energy usege as main point to achieve low-energy building

• We must know where we lose energy• Which values we must know before we start

to calculat heating energy usege• Also what we need to have before when we

start to make calculation.

Calculated enery usageHeating energy use per heating surface Degree days 3974°C/d

Balanced temperature=16.25 °C

Envilope Area m2 Estimated U‑value, W/(m2K)

Estimated heat loss kWh/a Percentage

Insulated exterior wall 739.46 0.26 18337

12.3Original exterior wall 867.00 0.26 21500

Roof 762.96 0.26 18920 5.9

Floor 762.96 0.25 18192 5.6

New windows 468.2 1.60 71448 22.1

Windows 17.02 1.60 25971.2

Exterior doors 8.36 1.60 1276

Volume m³ Air exchange rate Estimated heat loss kWh/a

Air exchange 8910 0.6 170810 52.9

Σ 323079

Heating energy use per heating surface 97.9 kWh/m2*a

Energy certificate

Low energy and nearly zero energy buildings

Free heat from sun

It depens on windows solarfactor

Possibilities for saveing energy

Through which part energy leave from house (throught envilops, exshausted ventilation air)

1. How big are envilopes thermal conductivitys2. How big are envilopes area3. What is ventilation air rate4. What is the free heat load on buildingTo get good analyses is needed to to take right

building volumes from construction project and accurate data on the indoor climate.

Potential of energy efficiencyHeating energy use per heating surface Degree days2542

Balanced temperature=12.28

Envilope Area m2 Estimated U‑value, W/(m2K) Estimated heat loss kWh/a

Insulated exterior wall+50 mm insultation 739.46 0.20 9023

Original exterior wall- 150 mm insulation 867.00 0.20 10579

Roof 762.96 0.20 9310

Floor-150 mm insultation 762.96 0.20 9310

New windows-with 3 glasses 468.2 1.00 28565

Staircases windows- exchange 17.02 1.00 1039

Exterior doors-exchange 8.36 1.00 510

Volume m³ Air exchange rate Estimated heat loss kWh/a

Air exchange with heat recovery (70%) 8910 0.6 32779

Σ 101115

Heating energy use per heating surface 30.6 kwh/m2*a

New energy certificate

Conclusion

Good knowledge of indoor climate building physics, heating and ventilation ensures the quality of energy calculations.

Thank you!!