Difference between revisions of "Thermal energy need in Helsinki Metropolitan Area"

Revision as of 09:57, 20 April 2009

Scope

Defines how thermal energy need will change in the future in Helsinki metropolitan area. Calculations are done by day degree method which is explained here; Heating consumption of buildings.

Definition

Data

In 2007 9751 GWh thermal energy was consumed in district heating buildings in Helsinki Metropolitan area. By using day degree method and statistics of population in the area and water consumption per inhabitant, we can calculate that of thermal energy 350 GWh was used to heat tap water.

Then overall heat transfer coefficient U was 16,08 kWh/m² in Helsinki, 14,04 kWh/m² in Vantaa, 15,44 kWh/m² in Espoo and 28,58 kWh/m² in Kauniainen. If we estimate that in district heating and other buildings have same overall heat transfer coefficient, then we can calculate that total thermal energy consumption in Helsinki Metropolitan area was 12 413 GWh in 2007.

For future scenarios we need to estimate how the outdoor temperature and buildings energy efficiencies will evolve. If we use Helsinki Metropolitan area Council (YTV) report of future changes in the area and floor area and population estimations in it, we can calculate that in 2025 thermal energy need is 15 150 GWh.

Taking global warming and building stocks improving energy efficiency thermal energy need can be made more accurate. By YTV's estimations in 2025 473 GWh thermal energy is needed for warm tap water and 14 650 GWh for heating buildings. If then estimated that outdoor temperature is 0,24 ^o higher than it was in 2007, then the energy needed for heating buildings is 13 976 GWh. Buildings energy efficiencies are improving all the time and in 2010 law will require 40 % better overall heat transfer coefficients from buildings. If then estimated that all new buildings and renewed buildings have 40 % better overall heat transfer coefficient, then thermal energy needed in Helsinki Metropolitan area in 2025 is 12 890 GWh. This would mean that in a year thermal energy need increases 52 GWh.

^[1]. ^[2]. ^[3]

Causality

Unit

GWh

Formula

Qh = U * A * (Tin-Tout) * t 
 where Qh = Heat flow from building to surroundings,
 U = Buildings overall heat transfer coefficient,
 A = Buildings total surface area (floor, walls and roof),
 Tin = Indoor temperature,
 Tout = Outdoor temperature and 
 t = Time period of the transfer. 

Thermal energy what is needed for warm tap water can be calculated as

Qw = cp,w * pw * qm,w * (Tw,warm - Tw,cold) * t
 where  Qw = Thermal energy needed for warm tap water,
 pw = Water density,
 cp,w = Specific heat capacity for water,
 Tw,warm = Temperature of warm tap water and 
 Tw,cold = Temperature of cold tap water.

Other thermal energy leaks are estimated to be negligible. A city’s need of thermal energy in a year can be then estimated to be sum of single buildings need of thermal energy. Thus a city’s total need of thermal energy can be calculated as

Qtotal = Qw + Qh
 where  Qtotal = Year need of thermal energy in city,
 Qh = Heat flow from building to surroundings and
 Qw = Thermal energy needed for warm tap water.

Result

See also

References