Heating, Ventilation and Gas Supply

The engineers of this speciality work on construction sites at enterprises and at various research and designing institutes. They design, calculate and construct heating, ventilating and air con­ditioning systems for apartment houses and office buildings, as well as for industrial enterprises, In case of need they make re­pairs of separate parts and whole systems.

The purpose of heating, ventilating and air-conditioning sy­stems is to create comfort conditions, the environment inside the premises which is characterized by four principal factors: tempe­rature, humidity, air purity, and velocity and air motion. Heating provides the necessary temperature while ventilating is respon­sible for the rest.

Heating. In order to maintain standard room temperature, the heating apparatus must supply heat to replace the lost through the walls, floors, and ceilings, and, in addition, the heat neces­sary to warm the cold fresh air used for ventilation. Heat is lost by conduction through walls, floors and ceilings, and by diffusion through cracks around doors, windows, etc.

System of Heating. Leaving stoves and fireplaces out of consideration, the systems ordinarily employed for heating may be classified as follows:

a) Hot air.

b) Steam.

c) Hot water.

Hot Air Systems. In a hot air system, heated air from the furnace is introduced through leaders, stacks, and registers into the room. This air is at a higher temperature than the room, and, flowing across the ceilings and down by the walls, heat abstracted until it is eventually cooled to the desired room temperature. Fresh warm air from the furnace then forces the air that been cooled to room temperature out of the room through cracks, fireplaces etc. A heat balance may therefore be written a follows: the heat given up by the entering air equals the heat lost by conduction.

The force which causes hot air to flow from furnace to room results from the difference in densities of the cold air outside and the warm air inside the furnace and pipes.

Advantages. A hot air heating system is cheap to install, has a low cost of maintenance, and is not hard to manage. Its opera­ting cost it little, if any, greater than that of hot water or system of equal capacity.

Steam and Hot Water Systems. A steam or a hot water heating plant consists essentially of the radiators, the boiler, and the system of piping connecting the former with the latter. Steam, orhot water, from the boiler is circulated through the piping and radiators; in these the steam condenses giving up its latent heat and the water gives up some of its heat, thus warming the rooms. In the usual hot water installation, the boiler, pipes, and radia­tors are kept full of water at all times, an expansion tank being provided to compensate for the increase in volume of water heated and to prevent explosions in case of generation of too much steam.

System of Piping. For steam heating the system of piping usually employed are the ordinary one-pipe system and the two-pipe system. In the former, but one connection is made to radiator, this connection serving both as an inlet for the steam and as an outlet for the water of condensation. Inthe latter, there is a supply pipe and a return pipe for each radiator, system is expensive and not used generally in steam heating except for indirect radiators which must always have two connections in order to function properly.

In hot water heating, although one-pipe systems may be used, it is considered the best practice to have a supply pipe and turn pipe for each radiator. Rules and tables for computing the size of pipe for both steam and hot water heating will be found in handbooks,

In selecting a heating plant for residences there must be considered the size, the type of building, the climate, the first cost and the cost of operation.

Ventilating Methods. Natural ventilation includes all ventilationwithout positive means for admission and escape of air. In buildings of ordinary construction, any room will rece­ive some ventilation whenever its temperature is above or below that of the surrounding air, by the leakage around the doors, win­dows, etc. In a room heated by an ordinary stove it is found that the air will be changed from one to three times an hour, even when no air is purposely admitted for ventilation.

Systematic ventilation is necessary in public buildings in which people congregate, such as schools, cinemas, theaters, etc. and provision must be made for the admission and escape of the air through flues or definite openings and for power for moving air. The air may be moved by expansion due to heat or by fans. The latter method is the one most used since it affords ventila­tion in summer as well as winter. Ventilation by fans may be ac­complished by forcing the air into a room or exhausting air from it.

Air Conditioning

The term air conditioning in its broadest sense means control of any or all the physical or chemical qualities of the air within a structure. More particularly, it includes the simultaneous control of temperature, humidity, purity of the air (dust, bacteria, odors, toxic gases, ionization) most of these factors affect in greater or lesser degrees human health or comfort. The term is broad enough to embrace what­ever other additional factors may be found desirable for maintain­ing the atmosphere of occupied spaces at a condition best suited to the physiological requirements of the human body.