Radiant Surface Data

Radiant surfaces allow you to model a wide range of radiant systems where water is passed through pipes in a panel or embedded in the construction, transferring energy to/from a building surface (wall, ceiling or floor). They can be used to model low-temperature heated only surfaces (e.g. heated floors), cooled only surfaces (e.g. chilled ceilings) or changeover systems which heated or chilled water is passed through pipes to provide heating or cooling depending on the zone load. They can also be used to simulate surfaces with buried electric heating elements.

See the Radiant surfaces tutorial

Three types of radiant surfaces are available in DesignBuilder HVAC:

 

Note an important advantage of the EnergyPlus variable flow radiant surface over the constant flow equivalent is that it is fully autosizable, which makes it much quicker to set up, especially for large models.

When using the 2-Detailed HVAC Detailed HVAC Activity data option, radiant surface systems will only control based on the radiant system controls defined for the component itself and not via the standard zone thermostat defined on the HVAC zone dialog. If the radiant system is serving a zone with forced air equipment, the radiant system will follow the priority order established by the zone thermostat but will still base its response on the controls defined by the user for the radiant system.

 

When using the 1-Simple HVAC Detailed HVAC Activity data option, radiant surfaces are controlled using the usual HVAC zone heating setpoint temperature controls.

Note: In zones in which radiant systems are included, at least one surface must be assigned a construction with an internal source defined, which incorporates details of the embedded tubing system. See Internal Source under Constructions for further details.

Radiant surface HVAC components are placed, edited and deleted at HVAC zone level. To edit the data associated with a radiant surface, you first need to select it by moving the mouse cursor over it and then clicking the mouse button to select it. You can then access the edit dialog by right-clicking the mouse and selecting the Edit selected component option or alternatively, select the Edit selected component tool from the toolbar.

Important Note 1: The internal source must be placed thermally closer to the inside surface than to the outside surface of the construction to allow it to be considered for inclusion in a zone's radiant surface system. In other words, if the thermal resistance between the inside surface and the internal source is less than the resistance to the outside surface then the surface is considered to be a valid radiant surface to be included with the zone next to the inside surface and will be simulated as such. This rule applies to surfaces adjacent to outside as well as internal surfaces.

Important Note 2: Internal radiant surfaces cannot control heating/cooling delivery to both adjacent zones. The radiant surface will be associated with the control system of the adjacent zone that is thermally closest to the internal source. The zone next to the outside surface (thermally furthest from the internal source) will of course still receive some heating/cooling from the source but the heat flow will generally be less and it will not be controlled.

Tip: To define which side of an internal surface is internal and which is external see under Layer order on the Constructions Layer data page.

Heated Floors

These systems typically use low flow temperatures of around 40-55°C compared with around 80°C for traditional low temperature hot water heating systems using radiators and convectors. Lower return temperatures enable more efficient operation using condensing boilers and heat pumps.

Tip: Heated floor radiant surfaces can be connected to hot water loops fed by boiler, GSHP or district heating systems. Note that when connected to GSHP systems heated floors can offer a very efficient system as the low delivery temperatures they require (typically 35°C) are well matched to the optimal operating conditions for GSHP systems.

 

 

Chilled Ceilings

Chilled ceilings are mounted within the ceiling to provide quiet, draft free cooling of the space below. Each unit is made up of a small bore chilled water pipe arranged in an S-shape and attached to the upper surface of a ceiling panel. Ceiling panels are typically of thin metallic construction but can simply be plasterboard. In some systems the chilled water pipes are embedded within the ceiling panel.

 

During operation, the panel is cooled through contact with the chilled-water pipework allowing it to cool the space through a combination of convective and radiant output (up to 40% radiant). An insulating mat is often placed above the chilled water pipework and panel to minimise uncontrolled cooling of the area above. It is up to the user to include any such insulation in the construction definition.

 

One advantage of chilled ceilings is that they can be placed in a shallow ceiling void enabling them to be used in buildings with low floor to ceiling heights. However, their limited cooling output makes them unsuitable for areas with moderate to high heat gains. The maximum capacity of chilled ceiling systems is in the order of 70 W/m2.

 

Chilled-ceiling systems require a separate ventilation system for fresh air supply.

 

Condensation of room air on and within the chilled ceiling can be avoided by shutting of chilled water flow based on room dew point temperature.

Tip: Chilled ceilings can be connected to chilled water loops fed by chillers , district cooling or GSHP systems.

Chilled ceilings vs Cooled beams

The images below (reproduced with permission from CIBSE) illustrate the difference between the cooled beams described here and chilled ceilings.

 

CIBSE KS03 Figure 12

 

CIBSE Guide H Fig 5.79

Tip: A useful resource on chilled ceilings and cooled beams can be found at https://www.feta.co.uk/uploaded_images/files/CBCA/Chilled%20Beams%20Brochure_Final%207%20%28web%29.pdf

 

 

Target Tab

When editing the attributes associated with a radiant surface component it is possible to apply the same changes to units in other zones in the same HVAC Zone group. To do this select the components on the Target tab of the edit dialog as required.