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Energy Systems > Memory Game > Flashcards

Memory Game Flashcards

1
Q

Name the 11 Weather Parameters & Units

A

➤ 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)

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2
Q

Weather Parameters can effect on process in what Order effects

A

➤ 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.

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3
Q

Sequential Modelling - 3 main facts

A

➤ Process comportment are replaced with input-output Relationships (Black Box)
➤ Itterative process allows convergence to an accurate solution

Diagram -

Parameters in \ \ \
Input—–> | component | —–> output

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4
Q

Sequential Modelling - 3 benifits

A

➤ Suitable system design (component sizing)
➤ allows checking to see components will work together
➤ allows testing and analysis for high-level system control strategies.

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5
Q

Sequential Modelling - 2 downsides

A

➤ Little info available on component information

➤ Input parameters are fixed and thus not valid for design conditions.

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6
Q

Simultaneous Modelling - 4 benifits

A

➤ 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.

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7
Q

Simultaneous Modelling - 1 downsides

A

➤ information often not available from manufacturers regarding component

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8
Q

Simultaneous Modelling - 3 Facts

A

➤ 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.

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9
Q

Ground Source Heat Pump Explination

A

➤ 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

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10
Q

HVAC - system simulation approaches

A

➤ 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
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11
Q

PDE - explicit definition & Limitation

A

second order derivative replace with central difference approximation
&
first order forward apprximation

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12
Q

PDE - implicit definition & Limitation

A

second order derivative is replaced with central differnce with an unknown temperature value in future.
first order replace with a backwards approximation

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13
Q

PDE - explicit & implicit difference

A

Explicit has related stability criteria - restricting the time and space steps usable.

Implicit - unconditionally stable with lower accuracy.

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14
Q

How does taylor series expansion influence use solving PDE

A

TSE allows first and HO derivative replacement with approximation on the differences associated.
manipulation and enables solution to be obtained.

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15
Q

What are the two main system modeling methods

A

Numerical method & Response function method

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16
Q

Differences between Numerical and Response Function method

A

RF - Simplifying assumptions to get analytical solution.
NM - Assumptions not required such as linearisation of parameter effects and time based parameters (not assumed constant)

17
Q

Name 2 sources of erros when solving ODE/ PDE

A

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.

18
Q

Steps when using Numerical Simultaneous modelling approach. And issues associated.

A

➤ 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

19
Q

3 energy conservation Equations and the component/finite volume types that are applicable.

A

➤ 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.

20
Q

Why use different solvers, instead of a single solver, when multiple FV exist?

A

➤ 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.

21
Q

Pick a Energy component and give a simple and detailed disretisation scheme.

A

➤ 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
22
Q

What is the use of a weighting factor in numerical methods.

A

➤ 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.

23
Q

Stages to formulate a numerical model. (3)

A

➤ disretisation into FV & use of TSE

➤ conservation eqn development per FV

➤ simultaneous solving

24
Q

Sections of the numerical model matrix (3)

A

➤ material E conservation
➤ Surface material E conservation
➤ Fluid E conservation

25
Q

Solving the Numerical Matrix (3)

A

➤ Equations are all linked
➤ multiple solvers or partitions to solve clusters are various intervals
➤ Itteritive or directs solutions are obtained.

26
Q

Complicated Numerical Matrix issues (3)

A

➤ Solutions need solved simitaneously

➤ Matrix topology needs indexing for the solver call up information as required

27
Q

Surface Admittance Definition

A

➤ material’s ability to absorb

➤ low value means absorbs less

28
Q

State the 2 Response Function method domains

A

➤ Hz & time

29
Q

What is the main differences between the two Response function methods.

A

➤ 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.

30
Q

Stages of solving with Response Function in Time domain

A

➤ 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.

31
Q

Stages of solving with Response Function in Frequency domain

A

➤ 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.

32
Q

Admittance Method Assumptions (3)

A

➤ 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.

33
Q

two major issues that must be addressed when selecting weather data

A
  1. selection of representative extreme and typical conditions (to test operational robustness); and
  2. adequate representation of overall severity (to test whole life performance).

Energy Systems (6 decks)

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