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The Chilled Ceilings module allows you to create a set of chilled ceiling types for placement in the building and then control each instance of a particular type using flow rates, set points, and other control parameters specific to each particular zone.

Toolbar icon for Chilled Ceiling Types list.

Chilled Ceiling Types may be used to model mainly radiant chilled ceiling panels, mainly convective passive chilled beams, or anything in between. A hydronic cooling loop in a chilled concrete slab can also be modeled using a Chilled Ceiling Type, however, care should be taken to modify the input values accordingly. Active chilled beams should be modeled on the airside network using a cooling coil and loop for induced airflow controlled in proportion to primary airflow.

The chilled ceiling module allows modeling of both cold-water flow and modulated temperature controlled devices. The program uses a simple parametric model that includes thermal mass and variable heat transfer with chilled ceiling temperature.

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Figure 2-70: Chilled ceiling dialog

2.19.1 Reference

Enter a description of the component. It is for your use only and the only restrictions are that it must be 40 or fewer characters in length.

2.19.2 Panel Orientation

Select an orientation for the panels: horizontal for mainly horizontal panels—i.e. the majority of the chilled surface faces down toward the floor; vertical for wall-mounted panels or those with surface area mainly perpendicular to the floor and ceiling.

Vertical beams are mainly convective and horizontal beams are mainly radiative in their cooling effect. The selected option therefore affects the default radiative fraction in the next cell. It is also used as a parameter to the Alamdari and Hammond convective heat transfer coefficient equations in the determination of the form of the variation of the convective heat transfer coefficient with beam temperature.

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2.19.3 Radiant Fraction

Warning Limits 0.0 to 0.9 Error Limits 0.0 to 1.0

Enter the radiant fraction of the heat emitted from the device. See Table 13 for some typical values.

2.19.4 Reference Temperature Difference

Units °C

Default 5 Warning Limits 2.0 to 20.0 Error Limits 1.0 to 100.0

The manufacturers data commonly gives the cooling output of the unit for a given reference room-unit temperature difference. Enter the reference temperature in this cell. For example, the data may state that the cooling output is 2.5kW for a unit-room temperature difference of 6K, i.e., when the unit is 6K below the room temperature. In this case enter 6 in this cell.

2.19.5 Cooling Output at Reference Temperature Difference

Units kW Warning Limits 0.35 to 100.0 Error Limits 0.05 to 9999.0

Manufacturers data commonly states cooling output for a given unit-room temperature difference. Enter this reference cooling output in this cell. For example the data may state that the cooling output is 2.5 kW for a temperature difference of 6K. In this case enter 2.5 in this cell.

The program uses this data to calculate an effective area for use in the calculation of the convective heat transfer as follows:

A standard convective heat transfer coefficient HCIs is first calculated for the standard panel-to-room temperature difference, ÙTb using the Hammond and Alamdari equations:

HCIs = F_HCIs(ORI,Tsb,Tsr,CHARL) where:

Tsr is the standard room temperature (set to 22°C) Tsb is the standard beam temperature (= Tsr - ÙTb) ORI is the Orientation

CHARL is the characteristic length (set to 0.1m) F_HCIs is a function implementing the equations The effective area, Aeff is calculated as:

Page 133 of 188 Aeff = Qstd x (1 - rf)

_________________________ HCIs x (Tbs - Trs)

Where Qstd is the standard heat output at Tbs and rf is the radiant fraction.

Note that the Alamdari and Hammond equations are used to set up the form of the variation of the convective heat transfer coefficient as the beam and room temperatures vary and not to calculate absolute values from first principles. When the beam is at Tbs and the room is at Trs, the convective heat output from the unit is Qstd x (1 - rf).

2.19.6 Maximum Cooling from Chiller

Enter the maximum input from chiller. Because of the way in which chiller loads are calculated in the program, a maximum chiller capacity cannot be specified. Instead, a maximum limit must be allocated to each chilled ceiling, cooling coil, etc. Normally the sum of all the maximum capacities of all the devices on a cooling circuit should equal the maximum capacity of the chiller.

2.19.7 Distribution Pump Consumption

This item is included to allow for the electrical pumps on a zone-level secondary (or tertiary) hydronic loop. Whenever the flow rate on/off controller is on, irrespective of the actual flow rate, then the full electrical power specified here is assumed to apply. This allows the modeling of zoned control of cold-water distribution to chilled ceilings using local constant- speed pumps. Alternatively, such when only valves and not pumps are use at the zone loop level, pump power can be included on the secondary chilled-water loop at the system modeling level.

2.19.8 Panel Material

Select the material from which the chilled ceiling panels or passive chilled beams are made (steel or aluminum). The material is used together with the 'Total weight' and the water capacity' to calculate of the total thermal capacity of the beam.

2.19.9 Panel Weight

Enter the weight of the panels, excluding the weight of water in the system. This data is used to calculate thermal capacity.

2.19.10 Panel Water Capacity

Enter the water capacity of the panels or passive chilled beams. This is used to calculate the thermal capacity.

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