B.3. Calculations of seasonal energy demand <br>

B.3. Calculations of seasonal energy demand

Program Instal-heat&energy can perform for one data set the calculations of heat losses and seasonal energy demand. Such connection of two calculation methods in one program will reduce the work expenditure required for project execution, on the other side the data must be prepared very carefully. As well the data taken over default by the program must be reviewed and controlled. It is also necessary to determine internal heat gains, if they are present in the building, which are required for correct performing of heat balance.

Calculations of seasonal energy demand are performed on the basis of norm EN 832:1998. These calculations are optional in program – they can be switched off.

- Evaluation of heat consumption of a building is based on assumption of constant temperature during heating season in heated compartments (stationary heating).

In program calculations the losses and efficiencies of heating system are not taken into consideration, for this reason such calculated seasonal energy demand is indeed a seasonal building heat demand. Seasonal heat demand does not take into account the primary energy, which is required in the heat source for covering of all heat losses of heating system, resulting from distribution, transfer, regulation of heating system and others. For this reason, as the energy demand, in meaning of this instruction, is understood the seasonal heat demand.

In a building there can be several thermal zones, which can have various values of analytical temperature or intensity of internal or external heat gains.

Thermal balance components

Energetic balance is determined with assumption of following components:

- heat losses by penetration and ventilation between internal and external environment,

- heat losses or gains by penetration and ventilation between adjacent zones in a building,

- useful internal heat gains from internal heat sources,

- useful gains from insolation,

Calculation procedure of seasonal building heat demand includes:

- declaring of climatic data,

- defining of compartments as heated or non-heated ones,

- defining of analytical temperature,

- assigning of compartments to thermal zones,

- calculation of heat losses in a building in specified time,

- calculation of internal heat gains,

- calculation of heat gains from insolation,

- calculation of coefficient of total heat gains utilization,

- calculation of heat demand in specified time.

Determining of limits and zones of heated space

Limits of heated space that are walls, lowest floor and ceilings or roofs separating heated space from external environment or from adjacent heated zones or non-heated spaces.

Heated space can be divided into thermal zones. If the heated is heated on its entire heating area to the same temperature value and occurring internal and external gains are relatively small or uniformly distributed in entire area of building, calculations will be performed in relation to one thermal zone.

If there are some divergences from these assumptions in the building, then the compartments should be assigned to several thermal zones. This is one of conditions for obtaining of proper calculations results of seasonal heat demand. It is important, that in one group are compartments with similar intensity of internal and external heat gains. That should be compartments with the same temperature.

A small departure from this rule is treating the flat with bathroom as one temperature zone. In effect, such declaration of belonging to a thermal zone does not have significant influence on calculations result, but we will obtain following benefits

- calculation of seasonal energy demand for a flat,

- performing by the program of ventilation air balance for a flat.

Heated compartments (with given internal temperature) and non-heated compartments (with internal temperature calculated by the program) should not be connected in one thermal zone.

Calculation of heat losses in a building in specified time by use of total heat gains utilization coefficient.

The User takes in program advantages of monthly calculations method, which enables calculation of heat demand for every month of heating season.

Applied calculations algorithm assumes a determined heat exchange within one month and neglects the accumulated heat or heat given up to compartment as a result of daily quick temperature changes. The h coefficient is taken into account in calculations, representing the utilization of total heat gains.

Heat loss in one-zone building or in one thermal zone (of a flat) during analytical season includes heat loss for ventilation and by penetration to external environment, their thermal zones or/and to non-heated spaces. In the program, for calculation of heat loss for ventilation a minimal air exchange is assumed, which is required because of hygienic and comfort requirements. Its default value is equal to 0,5 exchanges per hour for a thermal zone.

Calculations of total heat gains – from insolation and external heat gains

In calculations algorithm, the heat gains from insolation by transparent partitions are omitted. As surfaces receiving solar radiation, only windows are considered in the program.

An effectively collecting surface of glazed element, such as windows depends on collecting surface, corrective coefficient because of shading, covering coefficient, frame coefficient and total permeability of solar energy.

A corrective coefficient because of shading takes into consideration reduction of solar radiation in case of presence of such factors as:

- shading by other buildings,

- shading because of topographic reasons, (for examples hills, trees),

- standing out elements,

- shading by other elements of the same building.

Values of coefficients depend on shading angle of shading element.

Value of covering coefficient is given for windows. It depends on type of curtains and their location on inner or outer side of a window.

Physical dimensions of building construction

Physical dimensions of building construction should be conforming with calculations. It is possible to apply inner dimensions, outer dimensions or totally inner dimensions, but the method of dimensioning should be kept during all calculations. More information to this contains APPENDIX D. DIMENSIONS OF PARTITIONS APPLIED IN CALCULATIONS.

Floors on the ground

Calculations of seasonal heat demand require calculations of „characteristic dimension of floor”. It is defined as quotient of floor area to the half of floor perimeter:

B = A/(0,5 P)

As a floor perimeter should be understood here a part of building perimeter, measured in the outline of external walls, per specified thermal zone. The perimeter of floor on the ground should be determined by the User for every thermal zone. If there are several thermal zones or (and) a non-heated zone, then the perimeter of floor on the ground should be reduced by the length of walls on the zone limits or (and) on the limits of zones and non-heated space.