Final Year Project (Week 13)

Week 13

Design of PDF 

Due to the difference between PI control and PDF control, the design will not similar as what I learned before. In specific, the calculation of Kp and Ki could be explained as the notes shown below:

However, for the house model, the system time constant is very large and the closed loop transfer equation could be approximated to a more specific form. At the same time, the damping ratio could be presented, which is required to equal 1 for critical damping situation.

The theory that present above is based on a linear system. As for the 4th order heating system, the design method of PDF will be different, which is also a more general method. Hence, the value of "g" will be chosen as (1/3*tau), which means the controller time constant and is tightly relate to the SAP Responsivity. The next task is to find out the "CB", followed by designing a dynamic PDF controller for the heating system. It will be a great challenge. 

Final Year Project (Week 12)

Week 12

Pseudo Derivative Feedback control 

This week I have tried to integrate the ASHP & Radiator system model into IDEAS model, but the simulation results indicates a bad heating performance.

The reason is that original controller is designed for gas boiler not heat pump. So the task for me is to design a new control system for ASHP & Radiator system. However, the ASHP & Radiator is a 4th order system, which means convention PID controller is not the most suitable one. Compared with that, the Pseudo Derivative Feedback (PDF) control method is preferred for a nonlinear controller.
The comparison between PI control and PDF control is shown as below:

It can be seen that the PDF control could make the temperature tracking more accurate without damping and overshoot. However, the response time will be slowly, which is corresponding to the controller time constant and responsive. However, the design for the PDF is not easy like the basic theory, because the ASHP & Radiator heating system is a 4th order system. So the design of the PDF will be complicated, which will based on the state space equations of the whole heating system. Meanwhile,  an approximating method may be used for the design. 

Final Year Project (Week 11)

Week 11

Interim report

After a semester of work, the Final Year Project of mine has been completed as planned at the begin. A heat pump based heating system model has been completed with a good performance. The task for rest time this semester is to complete the interim report. For the next semester, the ASHP and radiator system will be integrated into IDEAS model for domestic heating task, a control system will be designed aimed a better temperature tracking and stability.

Final Year Project (Week 10)

Week 10

Simulation and analysis for the heating system model

After completing the heating system model, another necessary procedure is to test its performance via varies of tests. Based on the ASHP & Rad block, 5 sets of data has been tested for designed heating system,
the data vales are shown in Table below. The expression and analysis for results are mainly focus on ASHP,max, COP, HP, HW, Rad, Tin, Tw and Treturn. For all tests, the simulated time is 3600 seconds and integration starts from the 290 second. Meanwhile, the unit for temperature is Kelvin (K) and
for heat is Watts (W).

                                                        Test data for RIDE & Rad model
There are 4 tests in total have been simulated:
Test 1: the influence for initial value of external temperature
Test 2: the influence for initial value of room temperature
Test 3: relationship of internal heat transfer
Test 4: performance of heating system when integrated into IDEAS

The results shows that the value of COP, Max heat pump output and heat pump output are all vary with the change of outside temperature and room temperature. However, the value will be stable if other factors are stable or the target temperature is achieved. These results indicates the successful of the design of both heat pump and radiator system.
The heat transfer could be found from the temperature changes, which is shown in the table below:

However, according to the temperature tracking plots that has been shown below, the temperature is around the target value but not accurate enough. In other words, the temperature tracking is not stable, meanwhile, this phenomenon will becomes more obvious when integrating the heating system into IDEAS building model. A new controller system is needed for the heating system as well as series of debugging. That's the challenge for the next semester.

Final Year Project (Week 9)

Week 9 

Implementation of the heating system model

Based on the results of last week, the main task for this week is to complete the heating system model by using Simulink. This is also the target of the first half of Final Year Project. The completed model could be found as below.

It can be seen from the figure above, there are 7 blocks in total, which could be divided into ASHP and Radiator two basic parts. For the ASHP:

The block diagram of COP & ASHP,max

The block diagram of heat pump output

For the radiator system, the blocks is implemented directed from relative equations and hence will not be shown but only mention its name:

1. The block diagram of water

2. The block diagram of Tin

3. The block diagram of Rad

4. The block diagram of Urad

5.The block diagram of Treturn

Final Year Project (Week 8)

Week 8

Modification of the heating system model 

After a meeting with my supervisor Dr. John Counsell, a series of modifications are needed for my heating system model. Especially for the radiator system, the previous one is too ideally to apply to actual product design. In fact, for the ASHP heating system, the heat that produced from heat pump will transfers to water, which is flowing within whole system via pipes. Then the heat will be transferred to radiator fins and finally diffuse to the air in room. This procedure is satisfying previous theory, which indicates three heat transfer steps existed in the heat pump heating system. Standing on this points, the model that completed last week is no longer suitable for my project. With the help of Dr.John, a revised equation sets were obtained and could be used for a new model implementation. The details are shown below:

Based on these equations, a revised model could be completed with the help of Simulink platform. However, it is hard to schedule the model because of the existing of many loops. In order to simplify the actually handle work, I have made transfer there equations into several blocks with inputs and outputs respectively. By the way, the typical value for different parameters have been found by looking at previous papers and manufacturer's data.

Typical value has been attached here as a reference:
Thp = 5*60; % Time constant for ASHP (unit: s)
Arad = 8.0; % Area of radiator in dwelling (unit: m^2)
Mdotw= 0.7177; % Mass flow rate of water in heat pump (unit: kg/s)
Mw = 3; % Mass of water in the systaem in kg
Mrad = 100; % Mass of the radiator metal in kg
Cp = 4180; % water specific heat capacity at at approx 40C (unit: J/(kg*K))
Crad = 466; % Steel heat capacity (unit: J/(kg*K))
Uw = 30; % heat transfer coefficient for gas at high pressure and liquid outside tubes (unit: W/(K*m^2))
Gc = 10000; % the gain of compressor power (W)

Final Year Project (Week 7)

Week 7 

Implementation the Heating system on Simulink

Based on the equations and parameters' value that obtained last week, the Simulink model has been completed. It includes two basic level; the top level indicates the basic structure of the heating system, which consists with radiator and ASHP two subsystems. Meanwhile, the heating system is connected with the IDEAS model, in order to replace the original gas boiler heating system. Besides, the value of external temperature comes from a given data base and could be used directly. The schedule of the top level is shown below:

In details, the block diagram of radiator system is shown as figure below, the relationship is based on the equation of Treturn.

However, the relationship for the ASHP is more complicated than radiator because of a series of judgement of the value of required heat, in order to protect the heating system operated in a better efficiency as well as safety. The details of layout is shown below:

The model of the heating system has been completed, the next task is to testing its performance according to series of testing and simulation. A more complex task is to ensure its performance when connected with the IDEAS model. The reason is that all the components and value of IDEAS model, including the control system, are adjusted based on original gas boiler heating system. The task for me, is to design and modified it for the ASHP heating system.