Saturday, September 23, 2017

Halton Passive Chilled Beams

Halton's chilled beam system is an air conditioning system for cooling applications where good indoor climate and individual space control are appreciated. The passive chilled beam system utilises the excellent heat transfer properties of water and provides a good indoor climate energy-efficiently.

A passive chilled beam system can be designed to fulfil requirements for sustainable, energy-efficient buildings that provide flexible use of space and a healthy and productive indoor climate. A passive chilled beam system can realise excellent indoor climate conditions in terms of thermal and acoustic properties in a wide range of installation scenarios.

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Operation of the system
Chilled beam systems are designed to use the dry cooling principle, operating in conditions in which condensation is prevented by control applications.

Ventilation
Ventilation in passive chilled beam systems typically is arranged using mixing ventilation with ceiling or wall diffusers. Alternatively, floor diffusers can be used. In passive-service chilled beams, a diffuser can be integrated into the beam unit for air supply.

Cooling
Chilled water circulates through the heat exchanger of the passive chilled beam unit, resulting in relatively high cooling capacities. Passive beam operation is based on free convection in the heat exchanger. Passive chilled beam units with a higher proportion of radiation also exist.

Heating
Heating generally is realised with a separate heating system.

  • A separate heating system – e.g., perimeter heating – typically is used in passive chilled beam installations.
  • Window draughts due to radiation and downward convective air movement during cold seasons need to be eliminated.

Typical input values and operation ranges

  • Room temperature, summer 23..25 °C
  • Room temperature, winter 20..22 °C
  • Water inlet temperature, cooling 14...16 °C
  • Target water flow rate 0.02...0.06 kg/s
  • Sound pressure level < 35 dB(A)
  • Cooling capacity / floor area ... 80 W/m2 ...120 W/m2 *
  • Cooling capacity / effective unit length ... 250 W/m ... 400 W/m *
  • Separately for ventilation
  • Supply air temperature 16 ... 19 °C
  • Outdoor air flow rate/ floor area, offices 1.5 ... 2.5 l/s/m2 5 ... 9 m3/h/m2, meeting rooms 1.5 ... 4 l/s/m2 5 ... 15 m3/h/m2

Note * It is reasonable to study the room air velocity conditions carefully
Note ** It is reasonable to study the thermal conditions carefully

Ventilation and air diffusion arrangement

  • The supply airflow rate shall be high enough to remove internal humidity loads.

Cooling using chilled beams

  • Required cooling capacities should be no more than 60 ... 90 W/m2. With well-dimensioned integrated applications, capacities as great as 120 W/m2 can be realised.
  • Thermal properties of the external walls and window construction should be reasonable.
  • Airtight windows with effective solar shading are used.
  • The cooling capacity of passive chilled beams is typically 150 ... 250 W/m to avoid draughts in the occupied zone, especially underneath the unit. Operation shall be designed with conditions in the occupied zone in all seasons (winter, summer, and intermediate season) taken into account.
  • The flow water temperature (typically above 14 °C) must be sufficiently high to avoid condensation in all operation conditions. If necessary, the inlet water temperature may be adjusted to compensate for outdoor or indoor conditions. A condensation sensor should be located in each zone.
  • Water flow rates and pressure drops in chilled beams should be in line with chilled water pipework design and pumping cost target levels.
  • Passive chilled beams installed in a suspended ceiling always require sufficiently large openings in the ceiling for the induced room air path.
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