Partial model for air dampers with exponential opening characteristics. This is the base model for air dampers. The model implements the functions that relate the opening signal and the flow coefficient. The model also defines parameters that are used by different air damper models.
The model is as in ASHRAE 825-RP except that a control signal of
y=0 means the damper is closed, and y=1 means
the damper is open.
This is opposite of the implementation of ASHRAE 825-RP, but used here
for consistency within this library.
For yL < y < yU, the damper characteristics is:
kd(y) = exp(a+b (1-y))
where kd is the loss coefficient (total pressure drop divided by dynamic pressure) and y is the fractional opening.
Outside this range, the damper characteristics is defined by a quadratic polynomial that
matches the damper resistance at y=0 and y=yL or
y=yU and y=1, respectively.
In addition, the polynomials are such that kd(y) is differentiable in
y and the derivative is continuous.
The damper characteristics is then used to compute the flow coefficient k(y) as:
k(y) = (2 ρ ⁄ kd(y))1/2 A
where A is the face area, which is computed using the nominal
mass flow rate m_flow_nominal, the nominal velocity
v_nominal and the density of the medium.
ASHRAE 825-RP lists the following parameter values as typical (note that the
default values in the model correspond to opposed blades).
| opposed blades | single blades | |
|---|---|---|
| yL | 15/90 | 15/90 |
| yU | 55/90 | 65/90 |
| k1 | 0.2 to 0.5 | 0.2 to 0.5 |
| a | -1.51 | -1.51 |
| b | 0.105*90 | 0.0842*90 |
(The loss coefficient in fully closed position k0 is computed based on the leakage coefficient
and the coefficient in fully open position.)
P. Haves, L. K. Norford, M. DeSimone and L. Mei, A Standard Simulation Testbed for the Evaluation of Control Algorithms & Strategies, ASHRAE Final Report 825-RP, Atlanta, GA.
m_flow and dp that now need
to be added in each derived damper model.dpDamper_nominal and dpFixed_nominal.k0 by leakage coefficient.k0 and k1.v_nominal, but set the assignment of A
to be final. This allows scaling the model with m_flow_nominal,
which is generally known in the flow leg,
and v_nominal, for which a default value can be specified.v_nominal and variable area,
to simplify parameterization of the model.
Also added assertion statements upon initialization
for parameters k0 and k1 so that they fall within
suggested ranges found in ASHRAE 825-RP. This is for
#544.
Evaluate=true for use_constant_density.
This is a structural parameter. Adding this annotation leads to fewer
numerical Jacobians for
Buildings.Examples.VAVReheat.ClosedLoop
with
Buildings.Media.PerfectGases.MoistAirUnsaturated.
Buildings.Fluid.BaseClasses.PartialResistance,
Buildings.Fluid.Actuators.BaseClasses.PartialTwoWayValve,
Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential,
Buildings.Fluid.Actuators.BaseClasses.PartialActuator
and model
Buildings.Fluid.FixedResistances.PressureDrop.