## 6 Future Trends and Issues
### Demand Control Ventilation (DCV)
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Domain Area** & & **Achieving Strategies of Energy Efficiency Using Retrofitting** & **Ref.** \\ \hline
1. Correct system design & \(\bullet\) & The design should take into account the operational circumstances that occur the majority of the running hours. Optimization under these conditions will be more beneficial than calculation at a single extreme design point. & [23,25,198] \\ \hline
2. Control philosophy & \(\bullet\) & To guarantee low condensing temperatures are available during the part load operation, avoid fixed set head pressure control. & \\
**—**:**:**: & Auxilites pump with set speeds can be avoided if possible, and fan power should be lowered at low loads. & \\
**—**:**: & Ensure that defrosting is only used when absolutely necessary and that it is completed as effectively as possible. & \\ \hline
3. Optimize components & \(\bullet\) & Compressor and condensing units should be selected at normal running conditions. & \\
**—**:**:**: & Evaporator unit and temperature selection can be appointed based on human activities. & \\
**—**:**:**: & Temperature differences must be considered for the choice of heat exchangers. & \\
**—**:**:**: & Choose the appropriate refrigerant for application. If all other design parameters are optimized, the refrigerant’s impact on efficiency is expected to be less than 5\%. & \\ \hline
4. Proper installation & \(\bullet\) & Following the guidance of the manufacturers for installation, such as maintaining the distance between indoor and outdoor units, leveling between them, and providing adequate space for air circulation to heat reject and absorb. & \\
**—**:**:**: & It is required to have an accurate amount of gas charge that ensures no over- and undercharging. & \\
**—**:**:**: & Correct adjustment of the expansion valve. & \\ \hline
5. Operation and maintenance & \(\bullet\) & No secondary flow problem. & \\
**—**:**:**: & Ensure the cleanliness of filters, coils, and other components. & \\
**—**:**:**: & If all installed systems are operating correctly, it can be estimated that an average of 10\% energy savings can be achieved, reducing running costs. & \\ \hline
6. Energy efficiency lighting & \(\bullet\) & LED & [102,199, 200, 201] \\
**—**:**:**: & Task lights & \\
**—**:**:**: & Thammers & \\
**—**:**:**: & Sensors & \\ \hline
7. Intelligent BEMS & Building energy management System & [86,118,202] \\ \hline
8. BESS & Battery energy storage system & [203, 204, 205] \\ \hline
9. Renewable energy integration & Solar panels and wind turbines & [74,118,206] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._It is important to have adequate ventilation since it protects our health as well as our buildings. However, the ventilation and energy needed for optimal indoor air quality (IAQ) may conflict [212]. Therefore, one of the most energy-efficient ways to obtain the best IAQ is to use DCV. As shown in Figure 11[213], DCV is a typical concept in HVAC systems that uses signals from inside sensors to continuously match the ventilation airflow rate with the actual demand. Likewise, DCV refers to the control of mechanically supplied rates of external air intake into buildings based on occupant demand. A HVAC system is typically built and operated to keep the ideal environmental conditions in place in order to maintain acceptable thermal comfort and IAQ. In a recently constructed Swedish building, the effects of VAV ventilation on IAQ and the potential for energy savings were investigated. The VAV system can more efficiently satisfy thermal comfort requirements while using less energy than a CAV system. A VAV system combined with the DCV approach has become one of the most energy-efficient ways to ensure both optimal IAQ and thermal comfort as the DCV idea has evolved [214]. In [212], research on a multi-residential complex examines the energy-saving possibilities of a ventilation system with an air-cleaning unit and demand control.