Energy Analysis of the Existing Building

In order to find the near-optimal strategy for the renovation of the building, the mandatory data were added to the model. Table 4-4 shows a part of the input data, such as the building envelope

materials, windows, operational schedule, allocation of building activities, building systems, temperature set points, and DHW, which are added to the energy simulation tool.

Table 4-4. Sample input data of the building characteristics.

Description Characteristics

Roof Surfaces Flat roof U-value = 0.25 W/m2K. Exterior Walls Brick/ block exterior finishing

Windows WWR: 30% clear 6 mm glass, double glazing in some parts, Frame: Steel and Aluminum

Airtightness 0.3 ACH constant rate, ON 24/7 Operation Schedule 7:00- 23:00 Mon-Fri

Space Allocation Study spaces (classroom and atelier), office, mechanical and electrical room, restrooms, storage, and corridors.

Activity Educational Facilities (multi-use), Occupancy density: 1.0764 (people/m2), Winter clothing: 1.2 (clo), Summer clothing: 0.5 (clo)

HVAC System Fan coil units (4-Pipe), Air-cooled chiller, Boilers and chillers: on 24/7, Air systems shut off: 11:00 -7:00 a.m.

Temperature Setting 22°C cooling, 28°C cooling setback, 20°C heating, and 15°C heating setback Heating Natural Gas, Heating system seasonal CoP: 0.85, maximum supply air temperature:

45 °C

Cooling Electricity from grid, Cooling system seasonal CoP: 2.8–3.2, minimum supply air temperature: 12 °C

DHW Electricity from grid, Dedicated hot water boiler, Delivery temperature: 65 °C, main supply temperature: 10 °C, CoP: 0.85, Consumption rate: 10–20 l/m2_-day

The energy consumption results for the ES are calculated. Table 4-5 shows the heating results based on the outside temperature for the city of Montreal, for all visible thermal zones. The controlled temperature is 20.09˚C, radiant temperature is 15.84˚C, operative temperature is 17.97˚C and the outside dry-bulb temperature is -23.20˚C. Zone sensible heating is 79.08 kW, and heat losses dominated by the mechanical ventilation loss are -19.34 kW. The heat balance data in Table 4-5 show the breakdown of the heat losses. Figure 4-4 shows the daily cooling results for the hottest summer design weather conditions in Montreal. The energy tool calculates half-hourly temperatures and heat flows from each zone. Additionally, the results demonstrate a comprehensive overview of the heat flows, systems load, relative humidity, and total fresh air comfort conditions in each zone. The total site energy consumption estimates of the building components using the simulation tool is about 651,485 kWh, which is equal to 381 kWh/m2; while the actual energy consumption, based on the energy bills, was measured to be 611,479 kWh for the years 2014-2015, which reflects a 6.1% difference in the values. Comparing the results of the

calculation with the energy bills shows that the results of the energy model are accurate and within the acceptable level of discrepancy.

In fact, for the ES, the energy consumption per square meter is distributed according to the energy bill for the entire building (with an area of 11,511 m2), but the simulation software calculates energy consumption for the case study only (1,708 m2). In addition, there are some physical inconsistencies between the actual building and the simulated model (e.g., the exact location of the building and adjacent open spaces). Additionally, the detailed HVAC system, which is designed for the case study is slightly different from actual conditions (e.g., the conditioned floor area (CFA) and heat losses per square meter are different).

Figure 4-4. Energy calculation results (Cooling). Table 4-5. Daily energy calculation results (Heating).

Figure 4-5 shows the results of the annual Building Energy Performance Simulation (BEPS) of the existing building for temperature and heat gain. The higher number of time steps per hour, defined based on the preference of EnergyPlus, improves the accuracy. However, this increases the computational time. In this study, the defined time steps are ten minutes, because the model has a detailed HVAC simulation, which is consistent with EnergyPlus recommendations (DesignBuilder, 2016). The validation of the simulation models was checked using three procedures: (1) verify that the data are imported correctly into the model, ensuring that the changes at different parts have the anticipated effect; (2) summer and winter design weeks are simulated separately to generate hourly results. The analysis of the hourly results confirms the precise operation of the building and equipment, mechanical and natural ventilation, and fresh air; (3) annual simulation is generated based on monthly results and data distribution is controlled for the main zones. The results of the simulation show that the heating system is sufficiently sized to make the load at design conditions as the air temperature (blue line) never drops below the set point during the occupancy period and also never drops below the setback temperature of 15 ˚C (Figure 4-5(a)). The model also shows that the air temperature increased to around 26 ˚C in the afternoon over several weeks, so the building is probably overheated, therefore some changes to

(a)

(b)

(c)

(d)

the existing design or controls are required (Figure 4-5(a)). The heat balance graph (Figure 4-5(b)) shows that the heating system has fluctuations especially in winter, which is confirmed by controlling the Zone Heating graph (red graph) in (Figure 4-5(c)). Therefore, the system needs modification or repair to have more efficient outcomes (Figure 4-5(c)). Investigating the fluctuation in the total fresh air graph (Figure 4-5(d)) explains that the variance in the infiltration rate seems significant and should be considered. Although the infiltration rate is set to a constant value and it is based on the reference temperature, changes in the variations in the indoor temperature should be studied.

As mentioned in Section 3.2, the data collected were then validated by other methods such as a semi-structured interview, site visit, and analyzing the plans and sections of the building. The result of the TEC for ES, which is calculated by the BEM, is validated through comparison with energy bills, and ATHENA LCA simulation tool as described in Tables 4-6 and 4-9. This difference is considered acceptable.

Table 4-6. Cross-checking of the results.

TEC of Existing Situation (ES) (kWh/m2) Differences (%)

Energy Bills (Metering) 358 -

DesignBuilder (Energy Simulation Tool) 381 6.1

ATHENA (LCA Simulation Tool) 391 9.2