In the previous website section (“Calculation and heating schemes”) you have seen how a preliminary heat loss calculation of a house is performed. However, this calculation is just a part of a general heat balance of a house, where all other heat losses, as well as other heat sources, are included.
1. Premise humidity condition is of substantial importance, since it is closely connected to a heat condition. Optimal relative humidity of a dwelling room is around 50-60%. Humidity sources in a house are: cooking, washing and pressing, shower, bathroom, wet cleaning, plants, human body perspiration. Average family may produce up to 15 l of moisture in a house per day. In the air moisture is contained in a form of aqueous vapor and the maximum water content depends on the air temperature:
|Maximum water content
That means, for example, if at the air temperature of 20 C moisture content in a room is 10,7 g/m3, then upon temperature decrease down to 12 C, air humidity will become 100% and further temperature decrease will cause moisture condensation on the most cool house construction elements. Therefore, if during the cold weather period you leave your country house for considerable amount of time, take care to thoroughly ventilate all premises before leaving. Thus you will prevent construction elements from moisture condensation and save it from wetting, mould formation and putrefaction. Increased water saturation of cladding structure leads to increased heat losses, what is demonstrated with Fig.2.
2. Since our company is involved not only in heating equipment manufacturing, but also in heating systems construction, we have created a longstanding database of maximum average (by bearings) wind speeds and maximum average January temperatures of European part of the Russian Federation. Average temperature in European part of the Russian Federation in January is -3.6 C, wind direction (average, by bearings) is south-west.
Here is an example of wind influence on the total heat losses of a building with 2.5 bricks thick walls:
|Total heat losses, , %||100||116||123||139|
And now to positive factors...
1. Heat sources in a premise are electrical heaters, radio and TV-equipment, refrigerator, washing machine, iron, hair drier and other electrical devices. Significant heat source is food cooking. Look around – for example, knowing the number of light bulbs turned on and their total power consumption, as well as power consumption of other electrical equipment, it is possible to calculate approximate value of additional heat income of your house. For aforementioned example of a house with area of 100 m2 this amount is around 2-3 kW per hour..
2. Human body and domestic animals also emit heat energy, for example, at light, medium or heavy physical activity human body emits up to 172 W; 172-193 W and over 193 W, accordingly. Count by yourselves.
3. In nature a positive factor of a heat balance is represented by insolation (sun irradiation).
|Daily average air temperature increase in premise (oC)||December||January||February||March||April|
|For south-oriented premise||1,0||1,5||2,6||3,3||3,2|
|For west-oriented premise||0,1||0,2||0,7||1,4||2,1|
Temperature values in the table are calculated basing on statistical data of sun radiation influence intensity to walls and windows surface (W/m2) and its duration (in hours) at geographical latitude of 60 (Russian Federation, Leningrad region).
4. We seldom think of what comfort means if we feel fine and convenient, but thermal discomfort with cold legs, wind from the back and wet walls quickly make us upset and does not allow to work and to rest at full rate. All comfort conditions of dwelling house or working place could be described with technical parameters and therefore could be controlled and regulated.
|Type of activity||Optimum air temperature, oC||Allowed (comfort) temperature range, oC|
As a basic temperature during winter periods a temperature of 18 C is used for calculation of heat losses and choosing heat generation type (as recommended in reference literature).
Normative temperature drop between the air temperature inside a dwelling room, outer wall, camp ceiling and first stage floor should be not more than 6.4 and 2 C accordingly. Remember this and do not place thermometer at the outer wall, it will show incorrect values. From sanitarian’s viewpoint it is useful to reduce air temperature in a bedroom at night time by 2 to 3 C as it is connected with metabolism intensity.
You have learned basics of a building thermal balance. Using this knowledge, you will be able to choose appropriate equipment for heating of certain premise by your own, or to entrust this to professionals.