Install Instructions

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IM-PR 566442 1114 (Design Manual)

Appendix I Glossary

Air Changes: The rate of air leakage into a building:

One air change per hour means the entire volume

of air in the building is replaced with outside air

each hour.

Btu, British Thermal Unit: The amount of

energy required to raise one pound of water by

one degree Fahrenheit.

Cavitation: The formation of vapor pockets

when the pressure on a liquid drops below its

vapor pressure. Cavitation is very undesirable

in circulators.

Constant Circulation: Pump is active throughout

entire heating or cooling season to maintain

constant flow through heated area. Temperature

is controlled by resetting the water temperature to

match the desired output.

Circuit (a.k.a Loop): A portion of a radiant panel

typically consisting of PEX tubing that runs to and

from a manifold. The circuit may be one of many

circuits in a zone or could be a zone itself.

Dead Heading: An undesirable operating condition

in which a circulator is running, but all flow through

it is blocked.

Delta T (∆T): Temperature Difference

Design Temperature:

Indoor Design Temperature: The designed

indoor temperature for a given space

Outdoor Design Temperature: The set of

temperature, humidity and wind conditions

that is used to estimate the heating and

cooling loads for a dwelling

Direct Return: Parallel piping in which the first

branch connected on the supply is also the first

branch connected on the return. This may require

balancing valves to ensure each parallel branch

receives balanced flow.

Feet of Head: The common English units of

expressing the head energy of a fluid. The units

of feet represent the total mechanical energy

content of each pound of fluid and are derived from

simplifying the units of FT•lb/lb.

Fixed Flow Rate: Occurs when a circulator

operates at a single speed setting, which only

deviates when the circulator turns on or off.

Fixed Temperature Setting: Occurs when

a radiant heating or cooling source’s supply

temperature is at a single temperature setting,

which only deviates when the heating or cooling

source turns on or off.

Flow Rate: The volumetric rate of flow of a fluid.

For liquids it is often expressed in units of gallons

per minute (gpm). For gases, it is often expressed

in units or cubic feet per minute (cfm).

Flow Velocity: The speed of an imaginary fluid

particle at some point in a piping system. Common

English units for flow velocity are feet per second.

F-Value: Heat loss per foot of exposed edge per

degree of indoor-outdoor temperature difference.

F-values depend on slab R-value, the amount of

edge insulation (when installed), the placement of

the insulating material and the resistance of the

soil path.

Heat Loss: The rate of heat lost through a panel or

building from inside to out.

Hydraulic Separation: A design objective in

a radiant piping system that permits greater

temperature and flow control across circuits

through the use of closely spaced tees, a low loss

header or a hydraulic separator.

Hydronic: Of, or relating to, or being a system of

heating or cooling that involves transfer of heat by

a circulating fluid (as water or vapor) in a closed

system of pipes.

Infiltration: The unintentional leakage of outside air

into a heated space.

Infiltration Explanations:

Tight: All structural panels, corners, cracks,

joints and penetrations are sealed by

meticulous workmanship using some

combination of air barrier (film), taping, packing

and caulking. Window and door assemblies are

rated at less than 0.25 CFM per running foot

of crack at 25 mph (wind speed). Bath exhaust

fans, kitchen exhaust fans and dryer vents are

equipped with backdraft dampers. The home

does not have ceiling recessed light fixtures or,

if so, there is a negligible amount of leakage

around the fixture. No combustion equipment

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