Valentina Koukenska, Ivan Ivanov

Abstract: A program system for computing the thermal loss in buildings and premises in presented in this issue. Here, the methods for computing the thermal loss are tacked. The structure of the system and part of the dialogue interfaces are shown.

1. Introduction

Bulgaria is situated in the mild climatic zone and there’s an annual change of four seasons. During a definite part of the year, including winter and partially spring and autumn, it’s the necessity that urges us to heat buildings of different functions.

There are several ways of heating, but here, interns of conditions, the mast common of all are local heating and in larger urban areas – central heating.

According to the conjuncture the most common heating appears to be the local one, released by different devices and the use of solid fuel. This entails over – expenditure of heating energy, unequal distribution of heat in the given building in concern of time and place, maintenance and exploitation of a large number of heating devices and its discomforts.

The very these disadvantages of the local heating have recently given rise to our quest of new solutions, one of which is the charging of local heating. Apart from the fact that it compensates for the disadvantages, mentioned above, it also has some additional advantages such as: free choice of fuel depending on the prices during the given season, possibility for automatic control energy and its apportionment inside building.

To fulfill the necessity of the building and each one of the premises, there must be designed a heating installation. Generally specialist in thermotechnics and means money and time does it. The design of heating installations necessitates the computing of the thermal loss in each premise of the building. On a local level this computing is usually done manually and includes plunging into different guides in building and reference books of thermotechnics and building materials.

This paper presents the program system for computing the thermal loss of buildings and premises. Apart from the thermal loss, this system can provide the user with information for the energy or the amount of some given fuel needed for the heating of a definite building during the whole heating season.

2. Methodics in the calculation of thermal loss

The heat necessary for maintenance of the set thermal conditions in the premises is calculated as a sum of the thermal loss of head coeducation Q_t and infiltration of external air Q_i

Q=Q_t +Q_i W(kcal/h) (1)

Q_t and Q_i should be determinate by the following formulae (2) and (3)

Q_t=kF(t_n-t_u).z, W (kcal/h), (2)

where

k is coefficient of heat coduction , W/(m^{2 0}C) or kcal/(m²h ⁰C);

t_n- temperature of the premises, ⁰C;

t_u- calculating external temperature ⁰C.

F - heat surface, m²

Q_i = _i.P.C. (t_n-t_u).z, W(kcal/h) (3)

where

a is a coefficient of air permeability of a joint of an air-permeable element, 1m in length 1m;

l - length of the joints of an element, m;

P - characteristic of the premises;

C - characteristic of the building.

To calculate the heat needed for the compensation of thermal losses, some additions should be made: computing the thermal losses of the building due to its surrounding surfaces (walls, doors, windows and things like that) and infiltration of cold air; turning off in the heating’s course, outer walls and sky directions; thermal losses in pipelines and warming of water and steel masses after cutting off the heating for the night.

For the very calculating to be done, the architect – designer should provide the user with all the necessary building’s data, such as:

• lay out of the building and its neighborhood;
• main plans in scale 1:50 or 1:100 according to the size of the building, as well as the necessary sections;
• data for the building materials and the constructions of walls, floors, windows and other building elements.

The thermal losses of a building are equal to the total of the thermal losses of its premises under heating. The thermal losses of the separate premises constitute a sum of thermal losses of head coeducation through all their surroundings, amended by the additions for orientation and by the thermal losses due to infiltration.

The heat consumption for a definite period of time depends on the factors thermal isolation and the building’s accumulative ability, climatic conditions, duration of exploitation per day, claims of the dwellers in the terms of the temperature inside the premises.

For a single heating season the heat consummation can be fixed by the next formula

where