## 4 Methodology
### Analysis of an Upgraded Method of Operation of Various Building-Energy Systems
#### 4.3.2 Controlling the Heat-Recovery Air Handling Unit's Operation
1—supply air temperature sensor; 2—indoor air temperature sensor; 3—heater three-way heater mixing valve with actuator; 4—three-way distribution cooler valve with actuator; 5—controller; 6—heating water temperature sensor at the long-term heat storage tank output; 7—heating water temperature sensor at the short-term heat storage tank output; 8—cooling water temperature sensor at the long-term heat storage tank output; 9—three-way diverter valve with actuator for the heater; 10—three-way diverter valve with actuator for cooler; 11—cooling water temperature sensor at the short-term heat storage tank output. 3. This procedure is repeated until the condition \(\theta_{i}=\theta_{sp}\) is met. If this condition is still not met, the unit goes into cooling operation. In the cooling operation, cooling water from long-term cold storage is fed into the chiller. The indoor air temperature \(\theta_{i}\) is controlled to the desired value \(\theta_{sp}\) by changing the supply air temperature \(\theta_{s}\) by controlling the actuator of the three-way radiator manifold valve. The procedure is as follows:  
1. If \(\theta_{i}>\theta_{sp}\), the supply air temperature \(\theta_{s}\) must be reduced. The controller controls the three-way radiator diverter valve actuator, thus opening the direct path. This procedure is repeated until the condition \(\theta_{i}=\theta_{sp}\) is met. The heater and cooler control valves are controlled in sequence, the cooler control valve opens only after the heater control valve is fully closed and vice versa. In the future, it is recommended that a peak cooling source is designed, e.g., a heat pump, and a short-term cold store in case the desired indoor air temperature cannot be reached in cooling mode;
2. If \(\theta_{i}<\theta_{sp}\), the supply air temperature \(\theta_{s}\) must be increased. The controller controls the three-way radiator distribution valve's actuator, closing the direct valve path;
3. This procedure is repeated until the condition \(\theta_{TB}=\theta_{sp}\) is satisfied. Figure 13: The indoor air temperature control principle during the operation of the recuperative air handling unit. \(\theta_{i}\)—indoor air temperature; \(\theta_{sp}\)—indoor air temperature setpoint; \(\theta_{L\text{-}}\)_This_—output long-term heat store temperature; \(\theta_{S\text{-}}\)_This_—output short-term heat store temperature; \(\theta_{L\text{-}}\)_Tc_—output long-term cold store temperature; \(\theta_{s}\)—supply air temperature before regulator intervention; \(\theta_{s}\) —supply air temperature behind the controller intervention. For use in larger buildings, we recommend applying a drag control of the indoor air temperature according to the outdoor air temperature, which would mean a reduction in the indoor air temperature setpoint for the summer period and an increase in the indoor air temperature setpoint for the winter period. The outdoor air-temperature influence would be set separately for each plant. This would result in cooling energy savings and reduce temperature shocks as people move from the indoor to the outdoor environment and vice versa. It would also be advisable in buildings with large solar heat gains to introduce a minimum supply air temperature limit of 17 \({}^{\circ}\)C to avoid draughts. It is also recommended to design short-term cold storage for such buildings and a peak cooling source to cover thermal loads in cases where the temperature of the cooling water from the short-term cold store will not be sufficient to achieve thermal comfort in the cooling plant. Inductive and Analogical form of Creation Innovative Method of Realization of Ventilation with Heat Recovery Pipe-in-Pipe  
The pipe-in-pipe air exchanger implementation is not ideal in terms of heat exchange between the pipes and the adjacent soil as the inner pipe lies at the bottom of the outer pipe, Figure 14a. To eliminate this problem, we propose the application of spacer rings to ensure uniform airflow around the entire inner pipe (Figure 14b).