Thermostat, air

Experimental Procedure. A schematic diagram of experimental apparatus is shown in Figure 2. About ten of cylindrical glass bottles enclosed samples of same composition were set in a thermostatic air chamber. The samples melted perfectly by holding for about 2h at... 

Check for underventilation caused by obstructed vents, faulty dampers or other HVAC system malfunctions, or from problems within the occupied space. Furniture, papers, or other materials can interfere with air movement around thermostats or block airflow from wall or floor-mounted registers. If office cubicles are used, a small space (i.e., two to four inches) between the bottom of the partitions and the floor may improve air circulation. 

Check temperature and/or humidity to see whether the complaint area is in the comfort range Take more than one measurement to account for variability over time and from place to place. Check thermostat operation. Check whether the supply air temperature corresponds to the design criteria. Use a hygrothermograph (if available) to log temperature and humidity changes in the complaint area. 

In Europe, the gas safety controls must meet the requirements of CEN standards, including flame failure devices, solenoid control valve, pilot con trols, ignition and governor. Overheat-type thermostats and either a pressure switch or an airflow-proving device are fitted to ensure that the burner will cut off in the event of no air flowing through the heater, such as occurs with fan failure. 

Thermostatic control of the gas supply to the heater is required so that the air-off temperature can be controlled. This is achieved by a two-stage control that opens a valve partly on low rate and fully on high rate. 

Room air conditioner (self-contained) A rcxjm air conditioner complete with a direct expansion (dx) system condenser and evaporator fans, filtration, and thermostatic control. 

An air conditioning system uses an assembly of equipment to treat air. Normally the assembly includes a heating system for modifying winter indoor temperature and humidity a refrigeration system for modifying summer temperature and humidity, a means to maintain indoor air quality (i.e., air filters and fresh air intake) a method of distribution of conditioned air and a control system, such as a thermostat, to maintain desired comfort conditions. 

Many air conditioning systems use simple thermostats to cycle equipment however, more sophisticated control systems employing electronics and microprocessors can reduce energy consumption. 

During prolonged heat waves which can cause blackouts and brownouts, electric utilities always request that customers limit energy consumption by raising thermostats and turning off the air conditioning when not home. It is uncertain if these requests are heeded, and if they arc, it is uncertain whether conformity is out of altruism (help the utilities) or self-interest (save money). 

The furnace blower or boiler circulator pump starts up to send heated room air or hot water through the ducts or hot water pipes to the steam radiators, or hot water baseboard units, or individual room air registers located throughout the house. When the thermostat is satisfied that the room temperature has reached the set point, the burner shuts off. In furnaces, the blov er continues to run a few seconds until the air temperature drops to about 90° F, then the blower also shuts off. The furnace blower may come on again before the next burner start-up to purge heat out of the furnace, particularly if the fan has a low turn-on set point. The cycle... 

Some new features of furnaces available today include variable speed blowers, which deliver warm air more slowly and more quietly when less heat is needed, and variable heat output from the burner, which when combined with the variable speed blower allows for more continuous heating than the typical fixed firing rate. Distribution system features can be sophisticated with zoned heating which employs a number of thermostats, a sophisticated central controller, and a series of valves or dampers that direct airflow or water to different parts of the home only when needed in those areas. 

For general purposes, including firing hot water boilers and warm air space heaters, package burners are commonly used. In these, the burner is ready assembled together with all its controls and air fan. To install such a burner it is only necessary to connect up to gas and electric supplies and controls (thermostats, etc.). 

This means that thermostatic balanced pressure steam traps which open when their element senses a temperature somewhat below that of saturated steam at the pressure existing within the steam space are very effective when used as automatic air vents. They are connected to a steam space at any location where air will collect. Usually this means at any remote point from the steam entry, along the path the steam takes as it fills the steam space. 

As with all convective systems, warm air heating installations produce large temperature gradients in the spaces they serve. This results in the inefficient use of heat and high heat losses from roofs and upper wall areas. To improve the energy efficiency of warm air systems, pendant-type punkah fans or similar devices may be installed at roof level in the heated space. During the operational hours of the heating system, these fans work either continuously or under the control of a roof-level thermostat and return the stratified warm air down to occupied levels. 

Forced convective Far convectors These units give a high heat output for volume of space occupied by the unit, together with the ability to distribute the heat over a considerable area using directional grilles. May be used to bring in heated fresh air for room ventilation. Rapid response to conhol by individual thermostat. By use of variable speed motors rapid warm-up available in intermittent systems Altered fresh air inlet facility. Electric supply required to each individual unit. 2 to 25 kW. 

Unit heaters A unit with a large propeller or cenhifugal fan to give high air volume and wide throws. Louvers direct the air flow in the direction required. May be ceiling mounted, discharging vertically or horizontally or floor mounted. Can be used with fresh air Rapid response to conhol by individual thermostat by use of multi-speed motors rapid warm-up available on intermittent systems Altered fresh air inlet facility. Electric supply required for each individual unit. 3 to 300 kW. 

Make no excuse for checking whether the sun shines on the thermostats or someone has washed the floor. Another common occurrence is that while the room is not being controlled as specified, the plant appears to be operating correctly. Here a series of simultaneous readings of air flows and wet and dry bulb temperatures should be taken around the whole of the air circuit - on and off coil, condition after fan, condition at inlet grilles, etc. Referring these to a psychrometric chart will usually indicate where the fault or leak lies. 

Type of heating in use - Thirteen downdraft-type steam unit heaters, controlled by an optimizer and internal air thermostats. 

Individual room temperature control is difficult with warm air systems, as any temperature control damper is likely to pass air at all times. Air thermostats are not accurate detectors of temperatures and temperature overshoot occurs, with consequent increases in energy consumption... 

The unauthorized alteration of internal air thermostats and time switches ... 

Air-cooled condensers having two or more fans (Figure 6.2) may have a pressure switch or thermostatic control to stop the fans one by one. This method is simple, cheap, and effective. 

Since the purpose of a refrigeration or air-conditioning system will be to reduce or maintain temperature, a thermostat will usually be fitted to stop the equipment or reduce its capacity when the required condition is reached. The following types are in use ... 

In the first of these methods, the reduction in air mass flow is limited by considerations of distribution velocities within the rooms, so at light load more air may need to be used, together with more re-heat, to keep air speeds up. Within this constraint, any proportion of sensible and latent heat can be satisfied, to attain correct room conditions. However, full humidity control would be very wasteful in energy and a simple thermostatic control is preferred. 

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