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Types of Radiant Heat Systems

There are several types of radiant heat systems, and those that will be discussed here include:

Electric Resistance Heaters
Fin-tube Systems
and Radiant Tubing and Panels. 

 

Description

Radiant systems are so named because they transfer heat from medium to medium along a direct line of contact, or line of sight.  The properties differ greatly from convective systems, which heat through movement of heated air.  Unlike convective systems, radiant systems provide a relatively balanced heat distribution within a room.  Radiant systems control only temperature, and are used for heating.  

(reference: www.advancedcomfortsystems.com)

 

  1. Electric Resistance Systems

Components

This system is composed of wiring, resistors, and panels.  The medium is electricity.  These systems operate by an electric current passing from wires through resistors in a panel.  The current causes the resistors to heat up, which in turn causes the temperature of the panel to increase.  The panels are most commonly placed in the ceiling.  The ceiling is directly heated by the panels.  Heat is transferred to anything in the line of sight of the heated ceiling.

Advantages

Panels situated in the ceiling can be heated to a relatively high temperature, since there is little danger of someone coming into direct contact with the ceiling.  

The heating equipment is hidden from view, so it is desirable for aesthetic purposes.

There is no hot air pumped through the space to lower humidity or carry dust, allergens, or other contaminants.

Easy separation of areas into zones for better climate control.

Requires space enough for wires and panels as opposed to the space required for other larger heating mechanisms and ductwork.

Easy installation for retro-fit applications.

      Disadvantages

Because hot air rises, hot air can remain high in the space creating an uneven, uncomfortable condition.
Electricity is a relatively expensive fuel.
There is a slow response to the thermostat because heat must be transferred through each medium before it is apparent in the space.
These are not often used because they are inefficient

      Numbers

Cost:  Electricity is an expensive fuel
Max Watt Density: 250W/ft
(Reference: Stein)

 

  1. Fin-tube Systems

      Components

This system consists of a boiler, a piping system, and fin-tube terminal units.  The medium is water or steam.  For water systems, water is heated by a boiler, and then run through pipes through a fin-tube terminal unit.  The hot water transfers heat to the fin-tube.  The fin-tube, which has a large surface area, transfers heat directly to the air near the fins.  Heat is transferred to anything in the line of site of this heated air and fin-tube.  This system is commonly referred to as baseboard heating.  

This system can be arranged as a series loop, a one-pipe system, a two-pipe reverse return system, or a two-pipe direct return system.  Series loop systems are essentially one continuous pipe delivering hot water through all the terminal units in turn.  One-pipe systems deliver water through one main pipe connecting to each terminal unit by means of a valve and secondary pipes.  The two-pipe reverse return and two-pipe direct return systems have a main hot water pipe, delivering through valves to individual terminal unit pipes, which empty into a main cool water pipe.  

      Advantages

There is no hot air pumped through the space to lower humidity or carry dust, allergens, or other contaminants.
Piping does not consume as much space as ductwork.
Placement complements "cold-spots" for even heating in an area.

      Disadvantages

The various piping arrangements result in varying efficiency of the system.  Series and direct return systems may cause uneven distribution of heat.
The terminal units are visible.  Damaged terminal units may leave heated elements exposed to potentially burn people or cause damage to furniture or clothing. 

    Numbers

Temperature drop through system < 20 degrees F
Water Temperature Range: 120F to 210F
Flow Rate: 1gpm to 4gpm
Steam pressure: approx 10psi
Range of heat delivered per ft: 320 - 810 Btu/h ft (780 Btu/ft typical)
Typical Fin specs: 3/4 sq. in., 40 fins/ft
(Reference: Stein)

 

  1. Radiant Floor Tubing/Panels

      Components

This system consists of a boiler, a piping system, a circulating pump, tubing, and sometimes panels. Hot water is also the medium of this system.  Water heated by a boiler is run through pipes to tubes embedded in a concrete floor slab.  The tubes may also be run through panels, which could be placed in the floor or ceiling.    Heat is transferred from the water, to the tubes, to the floor/ceiling, to anything in the line of sight of the floor or ceiling.

 

Tubing in Floor                                                Panels in Floor

(reference: www.taunton.com)

 

      Advantages

Because hot air rises, a heated floor results in an evenly heated space.  There are no cold spots.
The heating equipment is hidden from view, so it is desirable for aesthetic purposes.
There is no hot air pumped through the space to lower humidity or carry dust, allergens, or other contaminants.
Easy separation of areas into zones for better climate control.
Temperatures are more moderate compared to other systems, resulting in longer equipment life.
Piping does not consume as much space as ductwork.
Easy installation for retro-fit applications.

      Disadvantages

Requires careful handling to avoid puncture during construction.
Each system must be custom engineered to each application, taking into account many loads and variables.

 

High-resistance floor covering may impede its performance.
For a floor system, furniture may block the line of sight and cause cold spots.

    Numbers

Sizes: to limit pressure drop and temperature drop, 1/2" ID tubing < 300 ft., 5/8" or 3/4" tubing < 450ft.
Tube Spacing: 6", 12", or 18" apart depending on several variables including water temperature, floor covering and loads.
Durability: Tubing pressure tested for 60psi for 24 hrs.
Cost: Typical pricing might be $1.75 to $2.00 per sq. ft.
(Reference: www.taunton.com)

 

 Uses

These systems are commonly used in residences and small commercial buildings, where climate dictates heat loads.  These systems are especially useful where winters are cold and summers are mild, and only a heating system is required.  Radiant heat systems can also be installed outdoors, in roofs and driveways for example, to melt snow and ice. 

These systems would not be suitable for larger buildings.  Larger buildings contain many zones, with many loads and demands.  Such buildings require systems which control heating, cooling, humidity, and pressure.