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. 

Final Year Project (Week 6)

Week 6

The implementation of ASHP and radiator system

The model of heating system includes heat pump and radiator two subsystems. For the AHSP, the heat requirement comes from the IDEAS model and will be provided by heat pump within its limitation. In other words, the operation of ASHP should not exceed the max value of heat output. The supplementary heater will works if the MAX(ASHP) has reached.
Based on this, the calculation of Qmax and COP is significant for the ASHP block, its equations have been found via previous paper as shown below:

The typical COP regression model and Qdot(factor) regression model relationship is expresses as plots and are shown below for reference. It can be seen the COP and Qdot(factor) are relates with the temperature of external and return.

Hence the Qref comes from a published data base, which is obtained from a testing of 30 heat pump units with each of 8 test points, the data could be checked as the table shown below :

 Besides, there existing another valuable parameter for the calculation of Max ASHP output, which named return temperature (Treturn). Treturn comes from the radiator system and derivation is explained below, which is based on the actual operation principle of radiator.

                                                                                                                                                                 
The "hrad" represents the heat transfer coefficient and hence we will dealing the Qdot(Required) equals to the Qdot(HS). Based on this relation, equations and typical parameter's value, the ASHP as well as the radiator system could be implemented on the MATLAB via Simulink. The implementation work will be completed by next week.                                                                                                                                                                                                                                                                                                                                                                                                  

Final Year Project (Week 5)

Week 5 

Implementation of Heat pump and radiator system

According to previous correlating papers, some notes on terminology has been found.

The COP is a significant value that indicates the quality of whole system, which is calculated by "dividing total heat delivered to the building by the electricity used by the ASHP unit". For my project, the accepted value of COP is within the range form 3 to 5.5. The other two equation will be used as a reference to judge the characteristic and performance of the whole heating system.
So the actual COP would varies with the source temperature and this could be explained via a deeper understanding of the ideally heat pump cycle:

At the same time, the rate of heat output of radiator system is another important parameter of the system, it is tightly connect with the heat pump output. In order to achieve a better performance, the chosen of parameter's value is important and will be referred some manufacture data base, especially the heat transfer coefficients and radiator area, capacity.

Final Year Project (Week 4)

Week 4

Internal operation of radiator system 

The task for this week was to figure out the internal heat transfer relationship of radiator system. Inside the radiator system, the heat of water will be dissipated to radiators steel fins and the simulation is shown in Figure as below.

Heat transfer process is corresponding to the heat transfer coefficient between two different substances. Hence the ASHP based heating system includes 3 heat transfer processes in total, first one is between refrigerant gas and water, the second is between water and steel fins, the third one is between radiator surface and room air.
The performance of the whole heating system will depends on every parameters of heat pump and radiator, which also relates to a series of equations. For this project, my target is to figure out the operation principle of both heat pump and radiator. Meanwhile, implement the heating system into the MATLAB and Simulink as a model. For the next semester, the work will focus on the combination of heat pump system and IDEAS building model, achieving a good temperature tracking and control.
The outcome of heat pump, radiator and IDEAS three components should be connected as the Figure shown below:

The basic operation is that IDEAS output the heat requirement based on SAP target and air temperature to heating system model, which will then calculate the heat output and start working. The heat will be transferred to room through radiator. The system will calculate heat requirement for next time step via control system as the room temperature change.