Difference between revisions of "Heating consumption of buildings"
(→See also) |
m |
||
| Line 146: | Line 146: | ||
Q<sub>h</sub> = U<sub>f</sub> * (T<sub>in</sub>-T<sub>out</sub>)dt | Q<sub>h</sub> = U<sub>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) | + | 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 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 | Buildings also need thermal energy for warm tap water. This can be calculated by a following function | ||
Revision as of 05:53, 14 April 2009
Contents
Scope
To define heating consumption of buildings. D↷
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:
Af = Ar Aw = nAf A = Af+Aw+Ar=(n+2)*Af
Buildings overall heat transfer coefficient per floor area is calculated as:
Uf = (Af/Af*Uf + Aw/Af*Uw + Ar/Af*Ur)/(A/Af) =[(1/n)*Uf + n*Uw + (1/n)*Ur)]/(n+2)
where Af is area of floor, Ar is area of roof, Aw is area of walls, A is area of building, which emits heat, n is number of floors in the building and Uf is the overall heat transfer coefficient of floor, Uw the overall heat transfer coefficient of walls, and Ur is the overall heat transfer coefficient of roof. Unit of areas are m2, unit of the overall heat transfer coefficients are kW/(m2 K).
Building overall heat transfer coefficients are regulated in Finnish building regulations, which are presented in following table
| 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 | > 17 °C | > 5 °C | > 17 °C | > 5 °C | > 17 °C | > 5 °C | > 17 °C | > 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 of the buildings is calculated as:
Qh = Uf * (Tin-Tout)dt
where Qh is heating consumption of the buildings (kW/m2/year), Uf is floor weighted overall heat transfer coefficient per floor area of building (kW/m2 K) and Tin is inside temperature and Tout outside temperature (K) in time dt.
Buildings also need thermal energy for warm tap water. This can be calculated by a following function
Qw = cp,w pw qm,w * (Twarm - Tcold )t
where Qw is thermal energy which is needed to heat tap water (kW/m2/year), cp,w is specific thermal capacity of water (4.1962 kJ/kgK), pw is density of water (1000 kg/m3), qm,w is volume of needed warn tap water (in Finland 180-224 (dm3/inhabitant)/day or 3,5 - 4,9 (dm3/m2)/day), Twarm is temperature, where the tap water is heated (60 oC = 333,15 K), Tcold is temperature of the cold water (4 oC = 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 28oC).
So buildings total need of thermal energy is
Q = Qh + Qw
Seasonal variation of heating consumption (Qh) can be evaluated also with monthly mean temperature differences.
Unit
kW/m2/year D↷
Result
References
Rakennuksen energiankulutuksen ja lämmitystehontarpeen laskenta[1]
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 [2].
