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Cooling Load Calculation

Last modified by Claudia Bless on 2026/08/26 10:21

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Variable            

Decides for what variable, "Max heat removed" or "Room unit cool", the maximum will be calculated.  For "Max heat removed" the heat removed through ventilation and infiltration is included. 

Internal gains

Part of the internal gains (heat from electrical light, occupants and equipment) used in the simulation.

Smoothing of schedule can be adapted here. Per default the value of the System parameters is linked here.
(5 = +/-1h; 0 = no smoothing - this function is valid for schedules of internal gains)

Weather

  • If user-defined design-day data has been selected in the Location object, the given data is presented for reference. For this case, you may select what month to simulate (for manually trying different solar positions).
  • When ASHRAE design-day weather data is used, the severity of the day can be selected by changing the Monthly cumulative frequency for dry-bulb max.
  • Also for the case of ASHRAE data, you may explicitly select which months to run. This can be done to speed up repeated calculations of the same month (only) or to force IDA ICE to run all months. The default algorithm tries to be smart, and will not run winter months if loads are decreasing towards winter.

Cooling load calculation

The dialog allows you to specify conditions for an automatic cooling load calculation. The typical purpose of the cooling load calculation is to size service systems for cooling, but one may also use the procedure to investigate overheating, i.e. how hot the building will get with no or limited mechanical cooling.

For the basics of performing a cooling load calculation, see Cooling Load Calculation and Results in the IDA ICE Getting Started manual. For an overview of predefined simulations, see also the Simulation tab chapter in the ESBO Manual.

The general procedure for sizing in IDA ICE is to first equip the model with infinite or large capacity equipment, run a simulation experiment and see how much cooling power was required for each room and air handling unit and that was delivered by the plant. If no cooling equipment has been installed, or if the capacity is insufficient, the building will overheat. There is no automatic checking or warning if a zone overheats (since overheating is studied in the same way) and it is therefore important that the user ensures that setpoints actually have been sufficiently met, when the purpose is to size equipment.

Three things will have to be considered:

  1. The level of internal gains that should be applied (normally 100% of gains that have been defined in the model)
  2. Climate data to be used
  3. The applied cooling load scenario

One approach that is favored in some countries is to use a so called design reference year (DRY), i.e. an hourly weather file containing some extremely hot periods. This approach is supported by the Cooling wizard. To use this, press More and then Design period using climate file.

Another method is to use so called synthetic climate data, i.e. extremely hot days that are based on a statistical analysis of local measured weather over many years. This is the default method of IDA ICE. The simulation of a selected hot day is repeated over and over (as an infinite-length hot spell) and the simulation is automatically terminated when the building is no-longer heating up from day to day and a so called steady periodic condition has been reached. This approach corresponds to the ASHRAE heat balance method.

A problem is that modern buildings with high performance windows and large internal gains may have overheating problems in unusual parts of the year, e.g. in the winter when the sun stands low. This means that a typical middle-of-summer sizing approach can render severely undersized equipment. In fact, many buildings will exhibit separate cooling peaks not only for individual rooms, but also for each air handling unit and yet another for the plant that generates the cooling.

From IDA ICE 4.7, the process of finding these individual peaks is fully automated. Beginning from the summer months, extreme days of each month, are simulated until all peaks have been found. A summary of all found peak cases is then presented and from this, individual cases can be opened and further examined. Note: The result of such a cooling load simulation will be a number of cases named by month, each one containing at least one peak (zone, AHU or plant). In order to examine detailed results, a whole monthly peak case must be loaded.