# A Decentralized, Flat-Structured Control System for Chiller Plants +
## 2 Decentralized, Flat-Structured HVAC Automation System
### Basic Unit
#### 2.1.2 Device Model  
**Chiller**. COP is usually used to express the operating efficiency of the chiller, i.e., the ratio of cooling capacity to power consumption of the chiller. Generally, it can be fitted as a quadratic polynomial of three variables [25], i.e., a ten-coefficient formula commonly used by chiller manufacturers. The specific expression is shown in Equation (1),  
\[\small COP=a_{1}+a_{2}\cdot PLR+a_{3}\cdot T_{la}+a_{4}\cdot T_{ent}+a_{5}\cdot PLR ^{2}+a_{6}\cdot T_{la}^{2}+a_{7}\cdot T_{mt}{}^{2}+a_{8}\cdot PLR\cdot T_{la}+a_{9} \cdot PLR\cdot T_{ent}+a_{10}\cdot T_{la}\cdot T_{ent} \tag{1}\]  
where \(PLR\) is the partial load ratio, \(T_{la}\) is the temperature of the water leaving the evaporator, and \(T_{ent}\) is the temperature of the water entering the condenser. **Pump. ** Firstly, a new variable, pump speed ratio \(w\) (\(0<w<1\)), is defined as  
\[w=n_{act}/n_{ent} \tag{2}\]  
where \(n_{act}\) is the actual running speed of pump, \(n_{ent}\) is the rated speed of pump. Then, the pumps operation curve at all rated and non-rated working conditions could be expressed as Equations (3) and (4),  
\[H=bQ^{2}+cwQ+dw^{2} \tag{3}\]  
\[\eta=j(Q/w)^{2}+k(Q/w)+l \tag{4}\]  
where \(H\), \(Q\), and \(\eta\) are the pump head, flow rate and mechanical efficiency at the rated speed, respectively; \(b\), \(c\), \(d\) and \(j\), \(k\), \(l\) are constants that vary with the characteristics of a specific pump, which can be obtained from the experimental data or manufacturer data under the rated conditions. **Cooling tower. ** Under normal circumstances, the cooling tower efficiency and the ratio between the condenser water mass flow rate and the air mass flow rate of the cooling tower can be combined into a polynomial curve [26], as shown in Equation (5),  
\[\eta=s_{1}+s_{2}\cdot\frac{m_{mat}}{m_{air}}+s_{3}\cdot\left(\frac{m_{mat}}{ m_{air}}\right)^{2}+s_{4}\cdot\left(\frac{m_{mat}}{m_{air}}\right)^{3} \tag{5}\]  
\begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Name** & \begin{tabular}{c} **Performance** \\ **Parameter** \\ \end{tabular}  & **Device Model** & **Operating Status** & **Set Value** \\ \hline Chiller & & & Automatic/manual state, start and stop state, cumulative running time, number of starts, cold COP, cold current ratio, evaporator inlet and outlet water temperature, condenser inlet and outlet water temperature, evaporation temperature, condensation temperature, evaporation pressure, compressor Import and export temperature, water flow switch signal, water side valve & \\ Pump & \begin{tabular}{c} Rated head, rated flow, \\ rated power, rated efficiency, on/off \\ protection duration \\ \end{tabular}  & \begin{tabular}{c} a, b, c, j, k, l \\ \end{tabular}  & \begin{tabular}{c} a, b, c, j, k, l \\ \end{tabular}  & \begin{tabular}{c} Automatic/manual state, \\ start/stop state, chilled water outlet water temperature, water flow switch signal, water side valve \\ \end{tabular}  \\ Pump & \begin{tabular}{c} Rated head, rated flow, \\ rated power, rated efficiency, on/off \\ protection duration \\ \end{tabular}  & \begin{tabular}{c} a, b, c, j, k, l \\ \end{tabular}  & \begin{tabular}{c} Automatic/manual state, \\ start/stop, frequency, head, \\ upper and lower limit of \\ running frequency \\ \end{tabular}  \\ Cooling tower & \ \begin{tabular}{c} Rated water quantity, \\ rated air volume, rated power, on/off \\ protection duration \\ \end{tabular}  &
\begin{tabular}{c} a1, a2, a3, a4 \\ \end{where \(\eta\), \(m_{mult}\), \(m_{air}\) are the cooling tower efficiency, condenser water mass flow rate and air mass flow rate respectively; \(s_{1}\), \(s_{2}\), \(s_{3}\), \(s_{4}\) are constants that vary with the characteristics of a specific cooling tower, which can be obtained from the manufacturer data or experimental data under the rated conditions.