Recently, I was asked how one might constrain a connector width in an instance parameter to be less than the width of solid it is hosted on. In the specific case, there are two solids, one representing the main body of the equipment, and the duct 'collar' on which the connector is hosted. The duct size must match the collar, and the collar must stay smaller than the equipment.
The formula below to control the collar size works just fine... however, when you select the family instance in the project, you can use the blue numerical control to set the connector width to something larger than the geometry... as you can see from the formulae, there is are no constraints on the actual duct connector sizes.
The problem is one of validation, not constraints/dimensions. As you can see in the revised parameters below, there are a couple of checks to make sure the duct size stays smaller than the section size. If the duct is modified to be bigger than the body, we force the collar length to 0, which Revit will not allow, and a error to the user will force them to undo the invalid setting.
How would you approach this problem?
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From the help file, it states: accounts for heating or cooling “credit” loads that take the form of negative loads. For example, heat that leaves a zone through a partition into another zone can be a negative load/credit.
To exapnd on this, look at a couple of fundamental examples.
In the case of a heating load, it is common to not include internal gains, such as people, power, and lights. The basic assumption being that these things may not actually be on or in the space to provide the gain.
However, if you want to consider the internal gains in a heating calculation, the ‘Use Load Credits’ option will do this for you.
For example, looking at a single zone, in the Use Load Credits case, you see the heating load is less due to the credits from the internal gains:
Click to enlarge image.
Taking a look at a cooling load case, in the image below, the two zones have different set points. Zone 1 is kept cooler; therefore, heat will “flow” from Zone 2 to Zone 1 (indicated by arrow 1). In other words, there is a load on Zone 2 due to Zone 1. Conversely, this means there is an internal loss from Zone 2 to Zone 1. However, if you don’t ‘Use Load Credits’ you don’t see this in your cooling load calculation. Arrow 2 on the tables below show the partition load, without the credit in Zone 2. Using load credits allows the reduction of the load in Zone 2, as shown by arrow 3.
Click to enlarge image.
Here's a quick demo of how to keep the text in a device symbol readable.
There is a simple tool available on Labs to help you select duct fitting tables, and to help you 'see' the information the tables are based on. Download here: http://labs.autodesk.com/utilities/AshraeViewer/
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