1. No category

Example 2
Enn Veesalu
How to calculate heat loading of
residential buildings?
1 TABLE OF CONTENTS
2
EXAMPLE 2 ................................................................................................................................................... 2
2.1
How to calculate heat loading of residential buildings ....................................................................... 2
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
1
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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Figure 2.3.2 shows us where and how to measure the height of the wall.
First we calculate the area of external walls without windows and doors areas. In the same way we calculate the floors
and sealing areas.
Figure 2.3.2 Cross section of model house
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In Table 2.3.2 we insert boundary surface areas (A) of rooms as calculated above
Table 2.3.2 Data of rooms
Boundary
surface (A)
m2
(U)
W/m2·K
Kitchen & Living room
35,35
0,28
WC & Washing room
14,95
0,28
Bedroom
16,66
0,28
Name of rooms
All external walls:
66,96
Boundary
surface (A)
m2
(U)
W/m2·K
(H)
W/K
Windows
7,26
1,4
10,16
Doors
3,78
1,0
3,78
Floors
47,46
0,28
13,29
Ceilings
47,46
0,22
10,44
(H)
Name of surface
W/K
9,90
4,19
4,66
18,75
Total heat loss coefficient HT = 56,42 W/K
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In the sample case in Table 2.3.2 we chose 0,28 as thermal transmittance (U-value) of external walls; 1,4 as U – value of
windows and 1,0 as U- value of doors. The calculating method and example calculation Example 1 of U - value can be
found in homepage Heat transfer.
2.4 DATA
Previously, we know that the heat loss coefficient (H) is the quantity of heat in watts per degree Kelvin (1K or 1°C
difference between interior and exterior environment) emitting from the building to the exterior environment.
Consequently, we need to know the air temperatures of exterior and interior environment in degrees K or Celsius. Then
we find the difference between air temperature in degrees of interior and exterior environment.
We have to know what interior temperature we need as recommended by national values, and what is the average
temperature of exterior environment per heating period. We also need to know the lowest design temperature of
exterior environment per heating period.
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2.5 CALCULATIONS
Now we find the heat loss (Φ). From Table 6.2 we take the value of total heat loss coefficient (HT):
The calculations of heat loss that we did above have results only in watts per unit 1K. Therefore, we need to know, how
long is heating period and calculate this period into degree days. By national standards the heating periods of various
countries are different. In Estonia the heating period is 220 days.
If our difference of average temperature (ΔT1) is 23 K in degrees between interior and exterior environment for heating
period then we can calculate heating degree days (HDD) and heating degree hours (HDH).
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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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