How do Instructions for designing heating systems? How do home heating systems work?

3. Downdraught
Downdraught is a reverse convection. Air coming into contact with a surface that holds a lower temperature, cools down, becomes heavier and descends.
Downdraught occurs mostly in the window areas, as the window has the lowest temperature in a room, but all the surfaces with a lower temperature than the room air causes downdraught. How much will depend on the difference in temperature.
The cold air descends to the floor where it stays. Radiators below the windows can remove the downdraught providing they cover the whole width of the window.
Heat emission through radiation to a cold surface, cold radiation, is often mistaken for down draught. The same measures apply on both down draught as well as cold radiation. To counter balance this, raise the temperature of the cold surfaces

4. Ventilation.
Ventilation removes impurities, such as small particles, odour and moisture, from the rooms. Odour and moisture are secreted from the human body, but they are also produced by cooking. The introduction of showers
in the apartments increases the moisture production greatly, and a brief and effective ventilation is required.
An easy way to ventilate is to simply open a window. If this is done briefly with a fully open window or even with cross draught, it is both efficient and cheap. If no extra measures are taken to insulate round the windows, these leaks are sufficient during the winter months, together with an efficient airing, to remove the odour and moisture.

5. Wind influences.
The air changes in the building increases when it is windy, and if one wants to preserve the room temperature at the set level, a higher flow temperature to the radiators is required.

6. Distribution of the heat.
In principle, the room temperature should be the same in all the rooms of a building. If roof and gable walls are not insulated, it should be possible to keep a somewhat higher temperature in rooms with roof and/or gable walls.

7. Domestic hot water.
Each apartment should have access to domestic hot water in the kitchen and in the bathroom. The bathroom should be equipped with a floor drain and a shower.
When a combined heating and power plant is in operation and is using the apartment, heating systems for cooling, the costs for a shower are small, but the value of hygiene and comfort is substantial.

8. Hot water circulation.
When the water in a riser for domestic hot water stands without tapping for a long time it will take room temperature. The first person wanting hot water will therefore run away a large amount of water before hot
water reaches the tap. If a small circulation pipe is laid parallel to the riser and connected with the riser at the top, a gravity circulation is obtained so that hot water always is available.

1. Heat requirement.
The heat losses in a building consist of:
- Transmission
- Ventilation
- Domestic water

2. Calculation of the transmission losses.
The transmission losses are losses through walls, floors, ceilings/roofs, windows and doors, arising due to the outdoor and indoor temperature differences.
The size of these losses should be calculated at the outdoor design temperature for the specific geographical area, for example 10C, and a room temperature of 18-20C.
The calculated transmission loss will always be considerably higher than the real value.
When starting up the system the real losses are to serve as a basis for the adjustments made.

3. Ventilation.
It is rather easy in buildings with mechanical supply and exhaust air, to calculate the heat requirement for the ventilating air. The size of the air flow and the specific heat content of the air are known as well as the
required temperature rise. These factors are multiplied and the heat requirement for ventilation is determined.

4. Incidental heat gain.
Incidental heat gain from other heat sources than the heating system have to be used to reduce the heat consumption. The incidental heat gain will give over-temperatures if the heat supply from the heating system is not reduced correspondingly. Thermostatic valves are well suited to use the incidental heat gains with a preserved room temperature.

5. The wind influence on the heat requirements.
The air change increases in the buildings in windy conditions. The harder the wind, the larger the air changes. An increase in volume of cold air supplied to the room has to be warmed up to room temperature.
Otherwise the room temperature will decrease.

6. Heat requirement per room.
The total heat requirement per room is equal to the sum of the transmission and the ventilating requirement. The size of the radiators and the required flow are determined according to this value, at maximum
load.
7. Control of the actual heat requirement.
The actual heat requirement for a building cannot be obtained until the building is built and the system is in operation. The simplest way is to meter the current flow and the flow and return temperatures. A multiplication of the temperature difference and the flow gives the heat
amount.
8. Domestic hot water.
The heat requirement for heating domestic water is rather easy to calculate, the flow multiplied by the temperature raise, but the size of the accumulated flow is difficult to determine.
The pipes for domestic hot water have to be made of copper or of heat resistant plastics.

Heating systems.
The heating system should be constructed and operated in a way that the stated requirements can be reached with regard to environment, comfort, operating economy and a low return temperature.

1. Heat exchangers.
Each building ought to be equipped with its own sub-station. It is appropriate in long buildings to have several sub-stations. The same applies to high-rise buildings, of more than 18 floors. These are however divided vertically.

Sub-station:
In the sub-station, the high temperatures in the primary system are converted to the level required by the system in the building. The systems are completely separated from each other, a fact which requires an expansion
system and a circulation pump to make the secondary system work.

Circuit diagram:
If there is only one heat exchanger in the sub-station, there are no problems in connecting it, but a parallel connection of the exchangers is recommended when it is a case of several exchangers. Then each system will have its own control equipment and expansion vessel, as well as circulation pump.

Expansion system
An open expansion system, with the circulation pump installed in the flow pipe, is a simple and practical solution.
There has to be room around the vessel for inspection and repair work.
The connection of the expansion pipe to the heat exchanger must not be equipped with a shut-off device.
Corrosion protection of expansion vessels.
The expansion vessel and the upper part of the expansion pipe should be made of rust-proof material.

Circulation pump:
Circulation pumps should be installed in the flow, which will guarantee that there is water in all the radiators when the pump is in operation. The pumps should be reliable and equipped with a tight sealing shaft that
requires no maintenance. It is advisable to place a unit for sludge separation after the pump, a filter for instance. The filter unit is constructed with shut-off devices so that it can easily be emptied of sludge.

Horizontal distribution pipe:
Definitions
The horizontal distribution pipes distributes the water from the substation to other buildings and/or risers.
Pipe material.
Standard pipes joined together by welding are used for the larger units.
The connection of valves and devices is made with flanges.
Smaller pipe installations are of threaded steel pipe and the sizes are adapted to standardized pipe threads.
Piping.
The distribution pipes can be laid as pre-insulated pipes, in the ground, under a building or hung from the roof in the basement of the building, depending on how the building is constructed.

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