View source for Heating consumption of buildings

{{variable|moderator=Pauliina}}
==Scope==

Presents day degree method, which is used to define heating consumption of buildings. {{disclink|Variable or method?}}

==Definition==

Heating consumption (Q) of buildings can be defined with knowledge of surface area of building, inside and outside temperature in certain time period, and heat permeability factors.
Easiest way to use heating consumption is to define it as floor area weighted calculation. 

Assumptions: 
 A<sub>f</sub> = A<sub>r</sub>
 A<sub>w</sub> = n(A<sub>f</sub>)
 A<sub>window</sub> = 15/100 * A<sub>w</sub> (By Finnish regulation windows covered area can be maximum of 50 % the 
 buildings frontage, typical value used is 15 % of the buildings frontage)
 A<sub>door</sub> = x * 2m<sup>2</sup> 

Buildings overall [[U-value|heat transfer coefficient]] per floor area is calculated as:
 U<sub>Total,f</sub> = (A<sub>f</sub> * U<sub>f</sub> + A<sub>w</sub> * U<sub>w</sub> + A<sub>r</sub> * U<sub>r</sub>  + A<sub>window</sub> * U<sub>window</sub> + A<sub>door</sub> * U<sub>door</sub>)/A<sub>f</sub> 
 =U<sub>f</sub> + [n * (100-15)/100 - x * A<sub>doors</sub>] * U<sub>w</sub> + U<sub>r</sub> + (15/100) * U<sub>window</sub> + x * 2m<sup>2</sup>/A<sub>f</sub> * U<sub>door</sub>

where A<sub>f</sub> is area of floor, A<sub>r</sub> is area of roof, A<sub>w</sub> is area of walls, A<sub>window</sub> is area of windows, A<sub>door</sub> is area of doors, x is number of doors, n is number of floors in the building and U<sub>f</sub> is the overall heat transfer coefficient of floor, U<sub>w</sub> the overall heat transfer coefficient of walls, U<sub>window</sub> is the overall heat transfer coefficient of window, U<sub>door</sub> is the overall heat transfer coefficient of door and U<sub>r</sub> is the overall heat transfer coefficient of roof. Unit of areas are m<sup>2</sup>, unit of the overall heat transfer coefficients are kW/(m<sup>2</sup> K).

Building overall heat transfer coefficients are regulated in Finnish building regulations, which are presented in following table
{| {{prettytable}}
| Part of building
| 1978-1985
| 
| 1985-2002
| 
| 2003-2006
| 
| 2007-2010
| 
| 2010-?
| 
|----
| ,
| Mass less than
| Mass over
| Warm area
| Half warm area
| Warm area
| Half warm area
| Warm area
| Half warm area
| Warm area
| Half warm area
|----
| ,
| 100 kg / m2
| 100 kg / m2
| &gt; 17 °C
| &gt; 5 °C
| &gt; 17 °C
| &gt; 5 °C
| &gt; 17 °C
| &gt; 5 °C
| &gt; 17 °C
| &gt; 5 °C
|----
| ,
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
| [W / m2 K]
|----
| Walls
| 0,29
| 0,35
| 0,28
| 0,45
| 0,25
| 0,45
| 0,24
| 0,38
| 0,17
| 0,26
|----
| Roof
| 0,23
| 0,29
| 0,22
| 0,45
| 0,16
| 0,45
| 0,15
| 0,28
| 0,09
| 0,14
|----
| Floor
| 0,23
| 0,29
| 0,22
| 0,45
| 0,16
| 0,45
| 0,15
| 0,28
| 0,09
| 0,26
|----
| Part which is against ground
| 0,4
| 0,4
| 0,36
| 0,45
| 0,25
| 0,45
| 0,24
| 0,34
| 0,16
| 0,24
|----
| Window
| 
| 
| 2,1
| 3,1
| 1,4
| 2,1
| 1,4
| 1,8
| 1
| 1,4
|----
| Door
| 
| 
| 0,7
| 2,9
| 1,4
| 2,1
| 1,4
| 1,8
| 1
| 1,4
|----
|}

Heating consumption per floor area of the buildings is calculated as:
 Q<sub>h</sub> = U<sub>Total,f</sub> * (T<sub>in</sub>-T<sub>out</sub>)dt

where Q<sub>h</sub> is heating consumption of the buildings (kW/m<sup>2</sup>/year), U<sub>f</sub> is floor weighted overall heat transfer coefficient per floor area of building (kW/m<sup>2</sup> K) and T<sub>in</sub> is inside temperature (usually used 17<sup>o</sup>C=290,15 K) and T<sub>out</sub> outside temperature (K) in time dt.

Buildings also need thermal energy for warm tap water. This can be calculated by a following function
 Q<sub>w</sub> = c<sub>p,w</sub> p<sub>w</sub> q<sub>m,w</sub> * (T<sub>warm</sub> - T<sub>cold</sub> )t

where Q<sub>w</sub> is thermal energy which is needed to heat tap water (kW/m<sup>2</sup>/year), c<sub>p,w</sub> is specific thermal capacity of water (4.1962 kJ/kgK), p<sub>w</sub> is density of water (1000 kg/m<sup>3</sup>), q<sub>m,w</sub> is volume of needed warn tap water, which can be estimated to be 40 % of total used tap water (in Finland 100-224 (dm<sup>3</sup>/inhabitant)/day or 3,5 - 4,9 (dm<sup>3</sup>/m<sup>2</sup>)/day), T<sub>warm</sub> is temperature, where the tap water is heated (60 <sup>o</sup>C = 333,15 K), T<sub>cold</sub> is temperature of the cold water (4 <sup>o</sup>C = 277,15 K) and t is time (1 year = 360 days). This can be also estimated by looking buildings thermal energy consumption in summer months, when there can be estimated to be only warm tap water use, because of outdoor temperature. Note that specific thermal capacity and density of water changes when the temperature changes. In calculations is used extrapolated value for the specific thermal capacity value (in 28<sup>o</sup>C).

So buildings total need of thermal energy is 
 Q = Q<sub>h</sub> + Q<sub>w</sub>

Seasonal variation of heating consumption (Q<sub>h</sub>) can be evaluated also with monthly mean temperature differences.

==Unit==
kW/m<sup>2</sup>/year {{disclink|Unit}}

==Result==

==References==

Rakennuksen energiankulutuksen ja lämmitystehontarpeen laskenta[http://www.finlex.fi/data/normit/29520-D5-190607-suomi.pdf]

Rakennusten lämmitys. Olli Seppänen. 2001, 2 päivitetty painos. Suomen LVI-liitto ry. Gummerus kirjapaino Oy, Jyväskylä 2001. ISBN 951-98811-0-7.

==See also==

Monthly mean temperature in years 1900-2000 at Helsinki Jyväskylä and Sodankylä [http://www.fmi.fi/saa/tilastot_4.html#5].

*[[BIOHER assessment]]
*[[CLAIH assessment]]