## 4 Energy and Environmental Evaluation of the System Retrofitting Variants
### Annual Consumption of Primary Energy  
From the point of view of implementing a sustainable energy management strategy, it was necessary to optimize the consumption of non-renewable energy vectors--i.e., to minimize primary energy consumption and reduce carbon dioxide emissions. In order to compare the effects of implementing, in the considered plant, a chilled water production system based on absorption water chillers with a traditional system based on compression water chillers powered by electricity, we calculated the consumption of primary energy and carbon dioxide emissions. The comparison was made exclusively with reference to the retrofitted part of the chilled water production system. In the case of the basic variant (Variant 0), the consumption of primary energy was calculated as follows:  
\[E_{P}=\frac{1}{\eta_{\text{TOT},0}}\cdot\frac{Q_{\text{ch},r}}{\text{SEER}_{0}} \tag{1}\]  
where: \begin{tabular}{l l l} \hline \hline \(E_{P}\) & - & annual consumption of primary energy for the purpose of producing \\  & & cooling energy, in MWh/a, \\ \(Q_{ch,r}\) & - & annual cooling energy production, in MWh/a, \\ \(SEER_{0}\) & - & seasonal energy efficiency ratio for a compression water chiller, \\ \(\eta_{TOT,0}\) & - & total efficiency of electricity production, transmission, and utilization. \\ \hline \hline \end{tabular}   
The total efficiency of the production, transmission, and utilization of the electricity vector in the case of compression water chillers was calculated as follows:  
\[\eta_{\text{TOT},0}=\eta_{\text{EL}}\cdot\eta_{\text{W}} \tag{2}\]  
where: \begin{tabular}{l l} \hline \hline \(\eta_{EL}\) & - & efficiency of electricity production and transmission in the Polish energy \\  & & system, i.e., 0.40, \\ \(\eta_{W}\) & - & efficiency of energy utilization in the facility, i.e., 1.00. \\ \hline \hline \end{tabular}   
In the case of Variants 1 and 2, the consumption of primary energy was calculated according to the avoided cost principle [30], making it possible to compare the consumption of primary energy in cogenerative circuits (CHP plants) and separate ones (the production of heat in heating plants and electricity in system power stations). In line with the above, the consumption of primary energy for Variants 1 and 2 could be calculated as follows:  
\[E_{P}=\frac{1}{\eta_{\text{TOT},1(2)}}\cdot\frac{Q_{\text{ch},r}}{\text{SEER}_{ 1(2)}}\cdot(1+e)-\frac{1}{\eta_{\text{TOT},0}}\cdot\frac{Q_{\text{ch},r}}{ \text{SEER}_{1(2)}}\cdot e \tag{3}\]where: \begin{tabular}{l l l} \hline \hline \(E_{P}\) & - & annual consumption of primary energy for the purpose of producing \\  & - & cooling energy, in MWh/a, \\ \(Q_{ch,r}\) & - & annual cooling energy production, in MWh/a, \\ \(SEER_{1(2)}\) & - & seasonal energy efficiency ratio for an absorption water chiller, \\ \(\eta_{TOT,1(2)}\) & - & total efficiency of steam production, transmission, and consumption in the \\ \(e\) & - & average annual electricity and heat co-generation ratio in the facility's \\ \(\dfrac{\mathrm{E}}{\mathrm{Q}}\) & - & CHP plant. \\ \hline \hline \end{tabular}   
The average annual electricity and heat co-generation ratio in a facility's CHP plant is an average annual measure of efficiency that indicates the amount of electricity produced relative to the amount of useful heat generated in the co-generation process. \[e=\dfrac{\mathrm{E}}{\mathrm{Q}} \tag{4}\]  
where: \begin{tabular}{l l l} \hline \hline \(E\) & - & the amount of electricity produced, in MWh/a, \\ \(Q\) & - & the amount of useful heat produced, in MWh/a, \\ \hline \hline \end{tabular}   
Ratio (**e**) indicates how many units of electricity are produced per unit of useful heat generated in the co-generation process. The total efficiency of the production, transmission, and consumption of the electricity vector in the case of compression water chillers was calculated as follows:  
\[\eta_{\mathrm{TOT,1(2)}}=\eta_{\mathrm{EC}}\cdot\eta_{W} \tag{5}\]  
where: