Energy Measurements

Btu (British Thermal Unit)
Energy required to raise the temperature of 1 lb of water from 60°F to 61°F at 1 atmosphere pressure.

The rate at which fluid is delivered to or required by a system, part of a system, or a piece of equipment, usually expressed in terms of volume per unit of time.

Differential Pressure
The difference in pressure between two points in a system.

Flow Capacity
The rated flow through a regulator under stated in let, outlet, and droop pressures.

Gage Pressure
(Psig or bar g) The difference between atmospheric pressure and the pressure being measured. Also written gauge pressure.

Gauge Pressure
Pressure reading as shown on a gauge (psig or bar g). The difference between atmospheric pressure and the pressure the gauge is measuring. Also written gage pressure.

Inlet Pressure
The pressure at the inlet opening of a valve (PI)'

Kilowatt (kW)
The SI unit of power. It is used to specify the thermal performance of a heater (kW Heat Produced) as well as the power energy it consumes (kW Energy Consumed). Kilowatts are used as energy measurement for heat output in gas appliances such as storage water heaters. Kilowatts are typically used in relation to electricity and have limited use within gas appliances although they are accepted as an additional marking for use on applicable gas appliances.

Kilowatt Hour (kWh)
The standard unit of sale of electricity; it is the equivalent power consumed by a purely resistive load of 1000 Watts (1kW) for 1 hour. Your electricity supplier will specify the price in your supply contract. This measurement is now often used for all energy types.

Maximum Operating Pressure
The maximum pressure existing in a piping system during normal operation.

The primary measurement of energy used in the Gas Appliance Industry. 1Kg of LPG will produce to 50MJ of energy.

Operating Pressure
The actual pressure at which a device operates under normal conditions. This pressure may be positive or negative with respect to atmospheric pressure.

Outlet Pressure (Reduced Pressure)
The pressure leaving the outlet opening of a valve (P2)'

Rate of Flow
The volume of material passing a given point in a system per unit of time.

Rated Working Pressure
The maximum allowable pressure specified by the manufacturer.

Temperature Rise
Difference between existing and desired water temperature. Number of degrees (ºC) water must be raised, whether from inlet or preheated water.

Thermal Efficiency
The rate at which heat exchange surfaces transfer heat to the transfer medium (e.g., air to water or water or air). It is typically measured as the ratio of BTU output of hot water to BTU input of fuel. Types of heat movement that impact thermal efficiency: Conductive/Convective heating surfaces also referred to as secondary or indirect heating surfaces including all surfaces exposed only to hot combustion gases. or Radiant heating surfaces also called direct or primary heating surfaces and consist of heat exchanger surfaces directly exposed to radiant heat from the flame. Radiant heat transfer is tremendously more effective than conductive/convective heat transfer and, contrary to commonly accepted belief, is where most of the heat transfer occurs in a boiler, furnace or forced air system.

Measurement of power. One watt is equivalent to one joule per second of energy (or one unit of power = one volt x one ampere).

Weight, Specific
The weight per unit volume of a substance. The same as density.

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