What is Radiant Heating?

Radiant Heating is a form of heat transfer. Radiant Heating Panels emit most of their heat via longwave infrared radiation as opposed to convection or conduction. The longwave radiation that is emitted from the Radiant Heating Panels travels through the air (without directly heating the air) to its surroundings of a lower temperature (such as walls, floors, desks and occupants) thus raising the temperature of these surroundings. A secondary effect of the longwave radiation being emitted from the Radiant Heating Panels is that the air is heated by being in contact with the warmer surfaces.

How does a Radiant Heating system work?

A Radiant Heating Systems emits heat similarly to that of the sunshine. If you were to stand outside on a hot summers day then you would feel warm and comfortable as the Radiant Heat from the sunshine is travelling through the air and warming your body temperature. However, if a cloud were to prevent the sunshine from reaching you then you would immediately feel colder, even though the air temperature hasn't changed, this is because the cloud is preventing the Radiant Heat from reaching your body.

This works the same way if you think about a Radiant Heating System in an office environment. The Radiant Heat that is being emitted from the Radiant Heating System travels through the air and heats up its surroundings of a lower temperature.

Is Radiant Heat expensive to run?

As illustrated in 'How does a Radiant Heating system work?' demonstrates that Radiant Heat is fairly instantaneous and as such is an ideal solution for heating large open spaces such as Sports Halls and other environments where you want to heat the occupants quickly without having the heat all the air first. Because Radiant Heating systems don't have to heat up the air first, it means that it drastically reduces energy usage and therefore can save you money.

This principle also applies to Office Developments, Hospitals, Schools, Universities, and Airports, hence why Radiant Heating is a popular solution for heating large commercial buildings.

What are Active Chilled Beams?

Active Chilled Beams are a water driven cooling (and heating if required as a 4-pipe unit) unit which is also powered by forced ventilation, also known as a terminal unit.

The circulation of chilled water through the aluminium finned block coil makes the aluminium fins cold (note: Chilled Beams operate above dew point, hence typically 14°C chilled water flow, thus no condensation tray or condensation pumps and/or drains required, unlike other HVAC equipment) and similarly low temperature hot water (typically limited to 50°C flow to avoid room stratification) for heating is circulated via separate copper waterways sharing the same aluminium finned block.

An Active Chilled Beam operates using a primary fresh air supply (each beam is connected to the mains ventilation duct work) to offer increased output from the coil (heat exchanger). Active Chilled Beams provide sensible cooling or heating to the space through induction and forced convection. An Active Chilled Beam is supplied with a primary fresh air supply (dehumidified primary fresh air) from the AHU and main duct work which is delivered through a pressurized plenum. The dehumidified primary fresh air supply from the AHU (which should be designed to handle the latent load) is delivered through nozzles in order to create a negative pressure behind the coil, inducing room air through the heating/cooling coil. The induced room air is then mixed with the primary fresh air supply and the conditioned air should be carefully discharged back into the space to ensure high comfort levels are maintained.

Active Beams should be utilized when sensible cooling, heating, and ventilation air are required. Typical applications are Education facilities, Commercial Office buildings, Hospitals, Hotel rooms, Laboratories and other environments that may have moderate to high sensible heat loads or building retrofits where space for new mechanical equipment may be limited are all good applications for Active Chilled Beams.

What are Passive Chilled Beams?

Traditional Passive Chilled Beams are water driven cooling units that usually rely on the natural 'Convection' process for heat transfer. The circulation of chilled water through the aluminium finned block coil makes the aluminium fins cold (note: Chilled Beams operate above dew point, hence typically 14°C chilled water flow, thus no condensation tray or condensation pumps and/or drains are required, unlike other HVAC equipment) and when the air in the room becomes in contact with the cold aluminium fins, the density of the air increases (cold air is heavier than warm air) and as such this heavier denser air falls to the floor directly below the fin coil block, thus displacing warmer room air which easily rises as lighter (less dense) upto to sides and rear of the cold fin coil block, thus repeating the process of the surrounding air becoming more dense as a continuous cycle whilst ever chilled water is circulated through the fin coil block.

It is usual to conceal the aluminium fin coil block (fin coil battery) either behind a perforated metal ceiling or in a perforated metal casing - this type of old technology (Frengers 'Convect' product) can achieve high levels of cooling in terms of Watts/linear meter, however care should be taken to limit the cooling to a maximum of 225 Watts/linear meter to avoid excessive air velocities in the occupied zone if good Thermal Comfort is a requirement (ie less than 0.25m/s air speeds). Frenger would only offer this old technology for transient areas if requested and in excess of 225 W/m required - see 'What are Radiant Passive Chilled Beams' for second generation passive beam solutions that can achieve 325 W/m with less than 0.25m/s air velocities.

What are traditional Chilled Ceilings?

Traditional Chilled Ceilings are metal ceiling tiles that have aluminium extruded heat exchange pipe seats bonded to the rear of the tile, into which a serpentine copper coil is inserted/secured and insulted so that all cooling is via the front of the tile facing into the room space which requires cooling. The Chilled Ceiling Tiles can reasonably be of any size and shape and usually flush mounted onto a linear or tartan beam grid.

Frenger are responsible for the worlds largest chilled ceiling (Shell Oils HQ on the River Thames, London) back in 1962 and this 1775 m2 Chilled Ceiling lasted over 50 years before being recently decommissioned, which is a testament to not only Frenger's high quality products, but also the technology (although see X-Wing® Radiant Passive Chilled Beams for next generation of technology). Traditional Chilled Ceilings provide most of its cooling effect by 'radiant absorption' (see radiant absorption cooling) which accounts for approximately 60% of total cooling effect and the other 40% by convention.

The higher the radiant quotient for cooling, the more comfortable the cooling effect, the only down side to traditional Chilled Ceilings is relatively low cooing duties in terms of W/m2 as although circa 90W/m2 of activated tile area, this nets out at circa 63 W/m2 on the floor area as only 70% of ceiling area can be activated due to rest of ceiling areas being occupied by ceiling beam grid to support the heavy tiles and lighting etc...

What is Radiant Absorption Cooling?

Cooling by radiant absorption is where the surfaces of the cooling unit have the ability to omit and absorb radiation. The ability to omit and/or absorb radiation is measured as an epsilon value, whereby 1.0 is the highest possible and 0.001 the lowest. Typically, unpainted aluminium has an epsilon value of 0.2 and matt white powder coated metal 0.95 and matt black powder coated metal 0.97. The surface area and surface temperature are also critically important.

Both traditional Chilled Ceilings and X-Wing® Radiant Passive cooling units have large surface areas of powder coated metal (0.95 / 0.97 epsilon value) that are cooler than the surfaces of the room and occupants being cooled. Where as fin coil batteries used for Convective Only Passive Chilled Beams have unpainted aluminium fins (0.2 epsilon value).

Radiant Equation

Surface Area x Surface Temperature x 5.67 x epsilon value

Note: 5.67 is a constant value, known as the Stephan Boltzmann constant.

Radiant Heating is by omitting heat energy, Radiant Cooling is by absorbing heat energy as the surface with the highest temperature interacts with opposing surfaces of a lower temperature, giving its higher energy to the surface with the lower energy to try to become in equilibrium. This is another reason as to why fin coil batteries have little by way of radiant cooling (or heating) as all aluminium fins largest surface areas are facing one another (not facing the room space) and all fins are already the same surface temperature, hence no radiant exchange possibilities even if the aluminium had a higher epsilon value if painted.

What are Radiant Passive Chilled Beams?

Radiant Passive Chilled Beams are a 'hybrid' between a traditional Passive Chilled Beam and a Radiant Cooling Chilled Ceiling. Chilled water is circulated through the Radiant Passive Chilled Beam such as Frenger's 'X-Wing®' unit which consists of a single serpentine sinusoid coil (X-Wing® has no joints in the copper coil to eliminate any risk of leaks) with 4 gilled aluminium fins mechanically joined to each waterway. The fins are equally spaced and run longitudinally to each waterway, thus forming an 'X' cross-sectional profile with a waterway in the centre, hence the name 'X-Wing®'.

As chilled water is circulated through the copper water pipes, the aluminium become colder than the room space, thus cooling any air that comes into contact with the cold surfaces, this is the convective quotient and this represents 60% of the total cooling from the X-Wing® unit. The other 40% of total cooling comes from 'radiant absorption' which cools the occupants and room space without the air movement that is associated with convective cooling, hence higher total cooling allowed with radiant convective cooling (325 W/m) as opposed to traditional convective only cooling which is limited to 225 W/m to avoid excessive air velocities - see 'What is radiant absorption cooling'.

Is there a condensation risk with Chilled Beams?

Chilled Beams should always be designed to operate using a chilled water (CHW) supply temperate of at least 1°C above dew point of the indoor room condition (i.e. operate with a dry coil) such to remove the risk of any condensation. For example, if you take a typical summer room design of 24°C at 50% RH indoor space condition then the dew point would be approximately 12.9°C so in this case the minimum CHW supply would need to be 14°C (over 1°C safety margin). In fact, a condensate drain pan facility (as typically associated with an old 1980's type induction unit) would only introduce significant extra cost to the project due to the additional condensate piping, and the requirement to regularly biocide dose condensate drain pans to prevent harmful bacteria (Legionella) and mold growth, all of which shouldn't be required with Chilled Beams that are designed correctly to operate with a dry coil.

What is the typical product lifecycle?

As our standard Chilled Beam products contain no moving parts, fans, motors etc. then the product life can be well in excess of 25 years if regular water quality checks are undertaken.

Do Chilled Beams provide minimal maintenance?

Our standard Chilled Beam products contain no moving parts, fans, motors etc. Therefore, this helps to reduce product maintenance to normally periodic visual inspections every 4-5* years for a typical commercial office application which can be significantly less than other HVAC units.

*The visual inspection period will be dependent on the type of project application (i.e. any health care applications may require more frequent visual inspections/ cleaning requirements).