Typed Formulae & Menu Options

Typed Formulae

You do not need to use the control conditions interface to create your formula. By selecting “Type formula” you can simply type the formula or edit an existing one. In the example shown below the control will give an “on” signal (1) when the external temperature is 3°C greater than the internal temperature.

To confirm that the formula created is valid for use in ApacheSim you can click on the Check formula button. This will report any errors in the formula.

Refer to later sections for a list of valid functions operators and constants.

Menu Options

Buttons on the ‘Modulating formula profile creation’ dialog provide the following options:

Create formula: generates a formula based on the specified control conditions

Check formula: checks that the formulae created is valid

Reset: resets all the drop down boxes to the original configuration

Save formula: makes a temporary copy of the current formula

Recreate formula: reproduces the temporarily saved formula

Help: shows the help file for formula profiles

Graph: shows a graphical output of the current created formula profile

OK: saves the profile to the appropriate row of the Daily Profile table

Cancel: exits the formula creation dialog without saving any formulae

Formula Variables

Formulae can contain any of the following symbols representing weather and simulation variables:

Weather variables

Variable	Description	Metric unit	IP unit
ws	wind speed	m/s	ft/s
wd	wind direction	degrees clockwise from north	degrees clockwise from north
to	outside air temperature	° C	° F
twb	outside wet bulb temperature	° C	° F
go	outside air moisture	kg/kg	lb/lb
rho	outside air relative humidity	%	%
igh	global radiation on the horizontal plane	W/m²	Btu/(h·ft²)
ifh	diffuse radiation on the horizontal plane	W/m²	Btu/(h·ft²)
idn	direct normal radiation	W/m²	Btu/(h·ft²)
toav24	mean outside air temperature over previous 24 hours	° C	° F

Room variables

Variable	Description	Metric unit	IP unit
ta	room air temperature	° C	° F
tr	room mean radiant temperature	° C	° F
tdr	room dry resultant temperature	° C	° F
ta_	adjacent room air temperature	° C	° F
g	room moisture content	kg/kg	lb/lb
g_	adjacent room moisture content	kg/kg	lb/lb
rh	room relative humidity	%	%
rh_	adjacent room relative humidity	%	%
sol	short-wave solar gain to room	W	Btu/h
co2	room carbon dioxide concentration	ppm	ppm
e1	room illuminance (sensor 1)	lux	fc
e2	room illuminance (sensor 2)	lux	fc

Notes:

· Variable names can be uppercase or lowercase, e.g TO(1) or to(1), but not mixed, e.g. To(1).

· The illuminances e1 and e2 are computed only when the link to Radiance is used.

· e2 is not an active variable yet and should not be used.

Other variables

Variable	Description	Metric unit	IP unit
ii	incident solar irradiance	W/m²	Btu/(h·ft²)

Described in section 12.7.4 .

The input variables, and in the case of an absolute profile the profile value, are interpreted in metric or IP units depending on the Units Type of the profile.

The room variables ta, tr, tdr, g and sol refer to the state of the current room, and the room variables ta_ and g_ to the adjacent room on the other side of a building element. If a profile formula containing a room variable is used in a context where there is no current room (e.g. an on/off controller) the variable is assigned the value 0. Note that a single profile containing room variables can be used in any number of rooms and the result of the formula evaluation will be particular to each room.

A room variable may be linked to a particular room by following its symbol with a pair of brackets containing the room index number. Please note they start from 1 so the index number will be the zone number plus 1. For example ta(12) is the air temperature in the eleventh room, as seen in the ModelIT Rooms browser. When this syntax is used, the room number must be a literal integer. If you modify the geometry or reorder your room list after creating formula profiles (which reference to room index number) you may need to update the information in the formula profiles.

Note that the room air solar gain may not be used by the blind and shutter operating percentage profile groups, but the ambient variables such as global radiation on the horizontal plane and direct normal radiation may be.

Exceptions

In addition to the variables described above, there is the exceptional case of a “surface variable” which is neither a weather variable nor a room variable. Currently, the only example of this is the solar irradiance incident on a surface, denoted ii.

It is like a room variable in that its evaluation is context dependent; the ii variable is evaluated in reference to the surface to which the formula is attached. Unlike some of the room variables, it has no corresponding function, the evaluation of which would yield the value of the variable in reference to another specified surface (as described in section 12.9). Therefore, the expression “ii(1)”, for instance, is always illegal.

Note that ii is currently only used in electrochromic control functions. It should not be used in any other context.

Formula Operators

The table below lists the operators that can be used in formula profiles. They include the common arithmetic operators and Parentheses ‘(' and ‘)’ can be used to define the order of evaluation. In general operator precedence is taken as the table below:

Operator	Precedence	Unary?	Usage	Description
-	1	Yes	-x	Unary minus operator
^	2	No	x ^ y	x raised to the power of y
*	3	No	x * y	Multiplication operator
/	3	No	x / y	Division operator
\	3	No	x \ y	Integer divide operator; divides the first operand by the second and rounds the result to an integer (rounding towards zero)
%	3	No	x % y	Modulo; find remainder of the division of x by y
+	4	No	x + y	Addition operator
-	4	Yes	x - y	Subtraction operator
>	5	No	x > y	“Is greater than” logical operator. Returns 1 if true, 0 if false.
<	5	No	x < y	“Is less than” logical operator. Returns 1 if true, 0 if false.
>=	5	No	x >= y	“Is greater than or equal to” logical operator. Returns 1 if true, 0 if false.
<=	5	No	x <= y	“Is less than or equal to” logical operator. Returns 1 if true, 0 if false.
!	6	Yes	!x	“Fuzzy NOT” logical operator. Returns 1-x, but subject to range [0,1].
&	7	No	x & y	“Fuzzy AND” logical operator. Returns min(x,y), but subject to range [0,1].
\|	8	No	x \| y	“Fuzzy OR” logical operator. Returns max(x,y), but subject to range [0,1].

Operators are processed in order of precedence. Operators of equal precedence are evaluated in left-to-right order. Brackets override the processing order, e.g., if ta=21, 3*ta-20=43, but 3*(ta-20)=3. If in doubt, use brackets.

Operators involving a test for equality (those containing the “=” sign) are for most practical purposes equivalent to the version of the operator without the equals sign.