Heating and Ventilation systems - Glossary of Terms

Automatic Bypass Valve

This valve ensures that there is an appropriate flow of water through the boiler, even though some of the radiator / zone valves maybe close. Check with the boiler manufacturer to see whether or not you will need one.

Balanced flue.

A ducting system which allows a boiler to draw fresh air from, and discharge gases to, the outside simultaneously.

Boiler Interlock

A wiring arrangement by which the boiler (and possibly its main pump) is prevented from firing because there is no heat demand, although the internal boiler tank has dropped below the set temperature.

Condensing boiler.

A high-efficiency, gas forced-air furnace that extracts the latent heat lost in conventional (ie. non-condensing) furnaces.

Conductive Heat Loss.

Calculate by adding the heat loss of each surface in the room: exterior walls, interior walls, windows, ceiling, floor. Each area is multiplied by its U-value and the relevant temperature difference (for internal floor/walls/ceilings it may be low).

Cylinder thermostat

Thermostat attached to a hot water cylinder to control hot water heat demand.

Damper motor

Actuator that controls the amount of airflow in an air conditioning duct.

Downward loss.

Adjustment to heat loss through floor as result of using under floor heating. If under floor heating is used, there will be no room heat lost through the floor (as the floor is hotter than the rest of the room) but certain heat from the actual system will be lost. This can be estimated as Net Area x U-factor x (T_UFH - T_GND).

Frost control, Frost thermostat

A device that overrides boiler/heating status when temperature drops below a preset limit , turning the system on.

Heat exchanger.

A device used to warm outside air using recycled hot air and thus saving heating fuel.

Honeywell "C-Plan".

Refers to a wiring scheme where hot water tanks is fed by gravity, so there is a single pump (no valves) feeding the heating.

Honeywell "S-Plan".

Refers to single zone heating system where hot water and heating feeds circulate in a close circuit. The hot water feed heats the temperature controlled hot water tank, the heating feed is directed to the radiators. Boiler is only on if at least one circuit demands heat (boiler interlock). Uses two 2-port valves and one pump to control the flow.

Honeywell "W-Plan"

It is the Y-plan (see below) but wired to give priority to the hot water

Honeywell "Y-Plan"

Refers to a single zone heating system where hot water and heating fees circulate in close circuit. The hot water feed heats the temperature controlled hot water tank, the heating feed is directly fed to the radiators. Uses only one 3-way valve and one pump to control flow.

Heat Loss.

The amount of heat lost from a room taking as a basis the set design criteria. For instance, if your design criteria is a room temperature of 20C at an external temperature of -5C, then you heat loss will be calculated for a temperature gap of 25C. Heat loss is made up of conductive loss (heat loss by walls, windows, etc.) and ventilation loss (heat loss by lost hot air) plus an adjustment for downward loss if under floor heating is used.

Humidifier/Dehumidifier.

A device used to add/remove moisture from the air.

Night setback.

Control feature which allows temperature to drop at night, but does not switch the heating off completely. It saves heating at night, while making start up in the morning faster.

Pipe Thermostat.

If the boiler is in an unheated room (garage, cellar), this thermostat is connected to pipes to prevent over heating due to other controls (for instance a frost control).

Pump overrun

A timing device that allows the pump to run for a while after the boiler has stopped to discharge very hot water from the boiler heat exchanger.

Return flow

Used in both hot water and heating systems - indicates the pipe that returns hot water to the boiler. In hot water systems, this arrangement is used in long runs to keep the water hot so there is little delay when you turn a tap on.

Single Pole Double Throw (SPDT) switch

A switch with three terminals, one which is common. The common can close the circuit with either of the remaining two terminals. Double Pole Double Throw (DPDT) has six terminals in a similar configuration: 2 common terminals can close the circuit with either of the remaining pairs. Automatic versions of these switches are used in heating, with one floating being a call for heating and the other a call for cooling.

Thermostatic Radiator Valves (TRV)

A valve installed in the flow pipe into a radiator which can be opened or closed based on the ambient temperature. Thus providing local control.

Thermostat.

A device which senses ambient temperature relative to a set point and in turns, switch a circuit on or off.

Ventilation Heat Loss.

The heat loss due to the loss of hot air due to ventilation. It is calculated by multiplying the room volume by the design number of air changes per hour (typically between 0.5 and 1.5), the temperature difference (to the external temperature) and the Heat Capacity of the Air (~ 3600 x 9.17 10^-5 J/KM³= 0.33)

Wet bulb Temperature.

A measure of the humidity in the air. A thermometer immersed in a wet cloth will drop in proportion to the amount of evaporation, this will in turn depend on the ambient humidity.

Zone (heating).

An area of your residence which is heated/cooled independently of the rest of house/space. Not to be confused with 'lighting zones', 'music zones or 'security zones'.

Zone valve.

A (normally) low voltage valve for water heating systems. In basic systems, the valve is controlled by a thermostat in the relevant zone so it can be controlled independently of other zones. If no central control unit is available, these valves have a 'end switch' which triggers the heating pump if open. On the other hand, only the last zone valve to close will turn off the pump.

Top