Memory Game Flashcards
Name the 11 Weather Parameters & Units
➤ Wet & Dry Bulb Temperature (C)
➤ Wind Velocity - Speed (m/s) & Direction (from North)
➤ Patmos (Bar or Pa)
➤ Long Wave Radiation net (W/m^2)
➤ Precipitation (mm)
➤ Direct Solar Radiation - G (W/m^2)
➤ Diffuse Solar Radiation - D (W/m^2)
➤ Cloud cover (%)
➤ Sunshine (Hr)
Weather Parameters can effect on process in what Order effects
➤ 1st degree effects where the change in parameter is directly linked to the process
➤ 2nd degree effect where a change will influence other parameters within the process.
Sequential Modelling - 3 main facts
➤ Process comportment are replaced with input-output Relationships (Black Box)
➤ Itterative process allows convergence to an accurate solution
Diagram -
Parameters in \ \ \
Input—–> | component | —–> output
Sequential Modelling - 3 benifits
➤ Suitable system design (component sizing)
➤ allows checking to see components will work together
➤ allows testing and analysis for high-level system control strategies.
Sequential Modelling - 2 downsides
➤ Little info available on component information
➤ Input parameters are fixed and thus not valid for design conditions.
Simultaneous Modelling - 4 benifits
➤ Incorporates description of the fundamental processes for each component
➤ Allows component design optimisation
➤ doesn’t relay on design parameters
➤ allows analysis of components and whole system performance.
Simultaneous Modelling - 1 downsides
➤ information often not available from manufacturers regarding component
Simultaneous Modelling - 3 Facts
➤ Components become Finite Volumes
➤ system obeys conservation laws
➤ can increase nodes at different levels ie) in heat exchanger another level of detail would be from adding nodes at inter tube passes.
Ground Source Heat Pump Explination
➤ Heat exchanger
- Environment heat Qconv - Wall Qcond - Qconv flow
➤ Compressor
- Applies pressure and temp increase
➤ Heater Element - Q out to environment via
- Environment heat Qconv - Wall Qcond - Qconv room
➤ Expansion Valve
- cools and condenses
HVAC - system simulation approaches
➤ Conceptual Modelling
- characteristic interactions are modelled without component details.
- ie) Air Con system - Flux exchange with constraints, limitations, controls
- Useful in Early stages
➤ Detailed Modelling
- Explicit model per component
- All components link and require simultaneous solving
- All flow is now got change detail generating the output data throughout the system.
- good for studying transient conditions
PDE - explicit definition & Limitation
second order derivative replace with central difference approximation
&
first order forward apprximation
PDE - implicit definition & Limitation
second order derivative is replaced with central differnce with an unknown temperature value in future.
first order replace with a backwards approximation
PDE - explicit & implicit difference
Explicit has related stability criteria - restricting the time and space steps usable.
Implicit - unconditionally stable with lower accuracy.
How does taylor series expansion influence use solving PDE
TSE allows first and HO derivative replacement with approximation on the differences associated.
manipulation and enables solution to be obtained.
What are the two main system modeling methods
Numerical method & Response function method
Differences between Numerical and Response Function method
RF - Simplifying assumptions to get analytical solution.
NM - Assumptions not required such as linearisation of parameter effects and time based parameters (not assumed constant)
Name 2 sources of erros when solving ODE/ PDE
Truncation error - round off with neglecting high order terms in the TSE
Discretisation error - error from using time steps to represent a continuously changing system.
Steps when using Numerical Simultaneous modelling approach. And issues associated.
➤ Disretisation componnents into finite volumes
- surfaces and exchangers compressors etc.
- issue: resolution needed against cost
➤ Conservation equations per FV
- HMAM
- issues: poor theory representation of links between components. Absent or inaccurate coefficients.
➤ Simultaneous Solution
- entire equation set (big matrix) solved per time steps for changing BC’s
Issues: equation sets incomplete needing specialist solvers.
Different time domain with different solution frequencies.
Presence of non- linear solutions and complex dependencies requiring itteritive solutions
3 energy conservation Equations and the component/finite volume types that are applicable.
➤ Material E conservation
- phase changes, material boundary lines, opaque/transparency surfaces.
➤ Surface E conservation
- room surfaces, asset component surfaces
➤ Fluid E conservation
- room air, air gaps, working fluids.
Why use different solvers, instead of a single solver, when multiple FV exist?
➤ Each domain will have its own equation type (linear, non-linear) abd have different frequencies.
➤ Inefficient to use one solver as it would mean lowest frequency common frequency used.
➤ Single solver would need to be able to incorporate and adapt to both linear and non linear equations.
Pick a Energy component and give a simple and detailed disretisation scheme.
➤ Heat Exchanger
➤ simple
- node pairs to show the input/output of the two fluids.
➤ complex
- Multiple nodes along the tubes and passes and in between the tubes to understand how the heat is lost across the length of the exchanger.
- allowing analysis of effectiveness and gradients
What is the use of a weighting factor in numerical methods.
➤ The weighting factor compromises between stability/accuracy w=0.5 1/2 of implicit and explicit approach is used/
➤ each application has its own requirements and W is chosen to the situation.
Stages to formulate a numerical model. (3)
➤ disretisation into FV & use of TSE
➤ conservation eqn development per FV
➤ simultaneous solving
Sections of the numerical model matrix (3)
➤ material E conservation
➤ Surface material E conservation
➤ Fluid E conservation
Solving the Numerical Matrix (3)
➤ Equations are all linked
➤ multiple solvers or partitions to solve clusters are various intervals
➤ Itteritive or directs solutions are obtained.
Complicated Numerical Matrix issues (3)
➤ Solutions need solved simitaneously
➤ Matrix topology needs indexing for the solver call up information as required
Surface Admittance Definition
➤ material’s ability to absorb
➤ low value means absorbs less
State the 2 Response Function method domains
➤ Hz & time
What is the main differences between the two Response function methods.
➤ Time domain
- Disretisation by Triangular or rectangular blocks.
➤ Frequency domain
- represents continuous fuction as a series of sine waves with
increasing Hz but decreasing Amplitude.
Stages of solving with Response Function in Time domain
➤ The given PDE/ODE is provided in the time domain and is converted into an imaginary domain through use of Laplace transformation.
➤ Mathematical operations allows for reduction is complicity and solution.
- Disretisation using triangular or rectangular blocks.
- Unit BC and Response function is combined in each block to get the URF.
- BC & URF pairs are added to get overall response.
➤ Conversion back into the time domain via inverse Laplace transforms.
Stages of solving with Response Function in Frequency domain
➤ Take excitation and apply to the Sine wave
➤ Obtain URF per sine wave
➤ Since the harmonics change and refract adding over the time to get the mean value.
Admittance Method Assumptions (3)
➤ BC - 24 hr mean value
- climate over time frame may be poorly represented
- casual gains may be clipped off in this period.
➤ Constant parameters/properties
- not realistic hence poor estimations achieved
➤ Solar gains
- Approximations based on factor assumptions such as geometry/shading/windows.
two major issues that must be addressed when selecting weather data
- selection of representative extreme and typical conditions (to test operational robustness); and
- adequate representation of overall severity (to test whole life performance).
