Hydronic Heating and Cooling Principles and Systems

Vocabulary flashcards covering core definitions, concepts, equipment, components, and procedures across Chapters 1 through 12 of Hydronic Heating and Cooling.

Hydronic System

A heating and/or cooling system that uses water or another fluid as a heat transfer medium to move heat from one area to another.

Gravity Hydronic System

A hydronic system in which circulation to the heating units is accomplished by the difference in the density of water in the supply and return mains.

Hypocaust

An early heating system utilizing a raised floor set on stacks of tiles called pilae.

Pilae

Stacks of tiles used in a hypocaust system to set up a raised floor.

Open Hydronic System

A hydronic system that is, at some point, open to the atmosphere.

Comfort

That condition in which the human body feels neither warm nor cool and is at thermal equilibrium with the ambient temperature.

Forced Convection

The use of fans and blowers to assist heat transfer by convection.

Dew Point

The temperature where the air is saturated and can no longer hold water vapor.

Relative Humidity

The amount of moisture in air compared to the amount of moisture the air would hold at the same temperature when the air is saturated.

Sensible Heat

Heat that causes changes in temperature that can be measured.

Specific Heat

The amount of heat in British thermal units required to change the temperature of one pound of a substance one degree Fahrenheit.

Superheated

The state when a vapor is heated to a temperature higher than its boiling point.

Pressure Drop

The term used to describe power consumed in moving liquids through pipes, terminal units, fittings, and other system components.

Milinch

A unit of measurement in hydronic system design that occurs in fairly large, whole numbers, eliminating the need for fractional values in calculations.

Water Flow Velocity

The speed water moves through a piping section, typically expressed in feet per second ($\text{fps}$).

Power Burner

A burner consisting of a forced air fan used to bring air under pressure into close contact with fuel.

Condensing Boiler

A boiler where heat exchangers are designed to extract latent heat from the water vapor found in hot combustion gases before the gases enter the flue.

Heat Pump

A mechanical compression refrigeration system that reverses the flow of refrigerant through a system to transfer heat from one area to another.

Aquastat

A device that controls the starting, stopping, and firing rate of a hot water boiler burner by measuring the temperature of the water in the boiler.

Flow Switch

A device utilizing a paddle to sense fluid flow and physically close an electrical circuit, allowing power to the boiler burner.

Chiller

A high-volume hydronic air conditioning device that cools circulating heat transfer fluid (HTF) for terminal unit use.

Compressor

The part of a mechanical refrigerating system that receives refrigerant vapor at low pressure and compresses it into a lower volume at a higher pressure.

Cooling Tower

A device used to reject heat from the water circulated through a building's water-loop system or chiller condenser.

Approach

The temperature difference between cooling water leaving a cooling tower and the wet-bulb temperature of air entering the tower.

Input Rating

The amount of heat produced by a boiler as fuel is burned, expressed in British thermal units per hour ($\text{Btuh}$).

Makeup Water Line

The cold water supply line to a boiler that is used for boiler filling.

Volute

The pump casing or body that contains the pumped heat transfer fluid (HTF) under pressure.

Closed Impeller

An impeller that has shrouds on both sides of the vanes.

Check Valve

A valve that permits fluid flow in only one direction and closes automatically to prevent backflow.

Triple Duty Valves

Quietly operating heavy-duty valves that perform all of the functions normally required on the discharge side of hydronic system pumps.

Static Suction Lift

The vertical distance liquid is raised by atmospheric pressure from the surface of a supply reservoir to the centerline of the pump suction connection.

Balancing Valve

A valve designed to regulate the rate of fluid flow through a hydronic piping system to meet system requirements.

Henry's Law

Law stating that the amount of air that can be dissolved in water at a given pressure depends inversely on the temperature and directly on the pressure of the water at a given temperature.

Cavitation

The flashing of pumped liquid into vapor bubbles and the subsequent violent collapsing of those bubbles as the liquid moves from suction to discharge through a pump.

Static Pressure

The pressure caused by the height of water above any given point.

Primary-Secondary Pumping

A means of interconnecting piping circuits so that the operation of one will not affect the other.

Authority Having Jurisdiction (AHJ)

An organization, office, or individual designated by a government organization with legal powers to administer, interpret, and enforce codes and standards.

Riser Clamp

A two-piece pipe clamp used to support vertical runs of steel pipe, cast-iron pipe, and copper tube.

Expansion Joint

A special fitting made for installation at any convenient point along a long run of pipe for the purpose of absorbing expansion and contraction.

Diversion Fitting

A fitting that creates a greater-than-normal pressure drop in a line in order to divert flow to another line.

Thermostatic Control Valve

A silent, efficient, nonelectric control valve that provides reliable temperature control for a hydronic terminal unit.

Gate Valve

A full-way valve used to regulate fluid flow in which a threaded stem raises and lowers a wedge-shaped disc that fits against a smooth, machined surface, or valve seat, within the valve body.

Trunk Line

The section of the main in a multiple circuit system that carries the combined capacity of the circuits.

Primary Circuit

The piping directly connected to the heat source or chiller inlet and outlet and to which the compression or pre-charged expansion tank is connected.

Zone

A section of a building that is controlled by one HVAC controlling device.

Series Loop System

A piping system that circulates HTF through a single main in which each terminal unit serves as a portion of the main.

Four-Pipe System

A piping system used where each terminal unit or zone may heat or cool independently of all other units or circuits.

Risers

Vertical mains or large vertical branches from which smaller branch lines are taken off to provide HTF to terminal units.

Tertiary Loop

An additional loop taken off of a secondary loop to provide HTF to an additional terminal unit.

Terminal Unit

A hydronic system component that transfers heat between the heat transfer fluid (HTF) flowing through it and the air in building spaces.

Panel Radiator

A radiator designed to function more efficiently and at lower HTF temperatures than a traditional radiator.

Unit Heater

A self-contained, forced-air convection heater that is not connected to ductwork and contains a fan, an HTF coil, and controls in one cabinet.

Environmental Unit

A terminal unit that includes a desiccant wheel to dehumidify air and an energy recovery wheel to separately control the humidity and temperature of conditioned air.

Commissioning

A formal assessment of the functionality and efficiency of a system.

Preventive Maintenance

Scheduled and unscheduled work required and expected to keep equipment in peak operating condition.

Scale

An accumulation of mineral deposits on a surface.

Charging

The process of purging air from a hydronic system while filling it with the appropriate HTF at the proper pressure.

Predictive Maintenance

The monitoring of wear conditions and equipment operating characteristics in order to predict potential malfunctions or failures.

Static Head

A function of the weight of HTF and the vertical height of the HTF in the system above a pump.

System Pressure Drop

The decrease in HTF pressure caused by friction between the HTF and the inside surface of piping as HTF flows through the piping.

Layout Drawings

Drawings of the floor plan of a building that show walls, partitions, windows, doors, fixtures, and other details that affect the placement of piping and terminal devices.

R-value

The measure of thermal resistance of a material or product.

Snow and Ice Melting

The controlled and forced phase change of snow and/or ice to liquid and vapor with effluent being drained away from a surface in a safe manner.