# Modeling Heat Consumption of an Office Building During COVID-19 Restrictions
## 4 Results
In Figure 2, the larger discrepancy in energy demand was localized during the first hours of the day, when the traditional model could not recognize employees' arrival. A focus on operational data visualized the peak, which was present at noon. After a firmware upgrade, the controller could utilize internal heat gains correctly to decrease energy consumption. The total daily HVAC heat demand values calculated with the help of a novel methodology and an actual one were 124.6 and 117.1 kWh, respectively. DHW now accounts for less than 14% of daily energy consumption. Total heat demand was also 36% less, which brought a 31% difference compared to the total heat demand calculated according to the traditional methodology. The error decreased since the predicted values differed less from the actual heat demand curve. This was achieved by applying corresponding factors from Equations (5), (11) and (13) to every hour when it was potentially real. Moreover, all of the buildings were now simulated according to the square floor plan and particular details, checking, for instance, whether windows were evenly distributed among the four external walls. That led to more homogenous thermal behavior of the building, which took place in reality across a 24 h period. The difference in total energy demand, especially in DHW heat consumption, was also due to the latest COVID restrictions limiting the number of employees. Being close to the heat demand profile meant the simulation had already become more accurate. This was also relevant since the methodology allowed for cutting the peaks at 8:00 and 21:00 (Figure 2). Using the correct tools for a simulation enabled utilizing control scenarios when the design indoor temperature was decreased during the night to 16 \({}^{\circ}\)C. The same applied when a flexible operation during the day (from 12:00 to 14:00) was implemented, i.e., the setpoint temperature was reduced to 14 \({}^{\circ}\)C. From 4:00 to 7:00, energy demand increased because of the gradual increase in DHW consumption and thermal transient processes once the scheduled night setback of the SH system power finished. That resulted in a difference in the total annual SH heat demand of 5-7%. It is worth mentioning that time stamps such as 4:00, 7:00, or 12:00 are provided as benchmarks and indicators only. To ensure coherent and cohesive operation, a setback should begin only when the higher return temperature arrives at the considered substation, and the substation may decrease the heat output due to a lower temperature difference between the return temperature and the required supply temperature [8]. The same but opposite goes to the discharge phase. Also, considering that the daily average energy supplied to cover the peak was approximately 0.15 kW (Figure 2), it represented a large fraction of the profile, highlighting the influence of the thermal masses. In the case of thermal inertia, the mass flow rate inflowing in an SH system almost does not change when a higher return temperature arrives, as opposed to the other substation scenarios. Instead, excessive heat is dumped into the building envelopes, while temperature waves may pass the pulse onto the return line. Like [PERSON] et al. [5], all the investigated scenarios were based on pre-set schedules. The abovementioned strategy also decreases DHW heat demand at a substation during non-space heating periods. Tap delay and, associated with that, water consumption on the consumer side (amount to be estimated) can be decreased if a solution with advanced control is used. However, additional heat demand and a high return temperature might occur [9]. Unlike that, [PERSON] et al. 's [5] limitation was that DHW was not included in the modeling. However, the DHW heat demand profile typically has morning and evening peaks, and ignoring them results in inaccuracy during modeling. Another example is clearly visible local peaks induced by individual DHW use and a manual indoor temperature setting through a TRV or air conditioning interface.