Example 2

Enn Veesalu

EXAMPLE 2................................................................................................................................................... 2 2.1

2.2

Input parameters ................................................................................................................................. 2

2.3

Symbols and units................................................................................................................................ 2

2.4

Data ..................................................................................................................................................... 6

2.5

Calculations ......................................................................................................................................... 7

3

Conclusion ................................................................................................................................................... 8

4

References and literature ............................................................................................................................ 9

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2 EXAMPLE 2 2.1 HOW TO CALCULATE HEAT LOADING OF RESIDENTIAL BUILDINGS

2.2 INPUT PARAMETERS In this sample calculation we use formulas of European standard "Heating systems in buildings - Method for calculation of the design of heat load "(EN 12831:2003) and European standard "Building components and building elements. Thermal resistance and thermal transmittance. Calculation method (EN ISO 6946:2008). Heating systems differ among the countries due to climate, traditions and national regulations. Therefore only the simplified calculation methods are described here. The aim of this educational material is to give basic knowledge. In some cases in these standards the source data is multiplied by coefficients in order to get more accurate results. The heat losses are calculated in steady state conditions assuming constant properties, such as values for temperature, characteristics of buildings, etc. Below Figure 2.3.1, we can see a simple house plan, based on which it is possible to calculate the surfaces of external walls, as well as the heated surfaces of floors and ceilings. When the adjoining room's temperature is +5 °C or below, then the heated adjacent surfaces are also considered as external walls.

2.3 SYMBOLS AND UNITS Table 2.3.1 Symbol

Name

Unit

A

area

m2

b

thickness

m

H

heat loss coefficient, heat transfer coefficient

W/K

HT

total heat loss coefficient

W/K

U

thermal transmittance

W/(m2·K)

l

length

m

λ

conductivity

W/(m·K)

T

temperature on the Kelvin scale

K

Tin

interior temperature on the Kelvin scale

K

Tex.des

exterior designed temperature on the Kelvin scale

K

Tex.avr

exterior average temperature on the Kelvin scale

K

t

temperature on the Celsius scale

°C

Q

quantity of heat, quantity of energy

W·hr

Φ

heat loss, heat power, heat load

W

V

volume

m3

L

air flow rate

m3/s

2

Figure 2.3.1 Layout of model house

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3 CONCLUSION As we see, the end calculation is very short, but we need to know a lot of input data. Our final result tells to us that the total heat loss is 6,85 MWhr per heating period and how much fuel material we shall need according to this value. And if we want to know how powerful our heating system must be, the power of heating system must equal the value of heat loss of the building. To be more precise, the heat loss and heat load of the building should be equal. As much as we lose heat through the walls, ceilings, floors, windows and doors, so much we also need to add the heat. By our example we need to install the heater with the power of 2,43 kW. In economic calculations it will be 144 kWhr/m2 per year. In Estonian climate and by the national standard this is quite a good result. How to find predicted heat and fuel quantity for residential buildings will be shown in the next volumes.

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4 REFERENCES AND LITERATURE 1. 2. 3. 4. 5. 6. 7. 8.

EN 12831:2003 Heating systems in buildings - Method for calculation of the design of heat load. EN ISO 6946:2008 Building components and building elements. Thermal resistance and thermal transmittance. Calculation method. EN ISO 7345 Thermal insulation. Physical quantities and definitions. Hagentoft, C.E., 2005. Introduction to Building Physics. Studentlitteratur, Lund, Sweden. Hens, H., 2007. Building Physics – Heat, Air and Moisture. Fundamentals and Engineering Methods with Examples and Exercises. Ernst & Sohn A Wiley Company, Germany. Kalamees, T., 2009. Hoone energiaaudiitorite koolitus. Ehitusfüüsika. Tallinn University of Technology , Estonia Timusk, J., 2006. Ehitusfüüsika kompendium. Visand v8. University of Tartu, Estonia. Trechsel, H.R., (Ed) 1994. Moisture Control in Buildings. ASTM Manual Series: MNL 18, PCN 28 – 018094 – 10, Philadelphia, PA, 19103.

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