Summary of the second retrofitting

A church is similar to either classrooms or theatres where many converge for various programs. However, the assumptions made in this case, especially the chapel, were that there is often one person per 2 m². For instance, in a school, rooms are designed for teaching activities and are ventilated to a certain degree. With an airflow of 4 to 5 l/(S.m²), the CO2

concentration can be maintained at around 1000 ppm. This corresponds to the specific airflow around 5 to 6 h-1. However, the required airflow will be less if the rooms are high or the classes have fewer pupils per m² [8].

Since the Chapel is 7 m high with a surface area of 438 m² and occupied by 80 persons on Sundays in the building, it can be assumed as follows:

438m²/ 80 persons = 5.475 m²/person

Since the roof is 7000 mm high in the Chapel (the biggest area in the church) and has an occupant level of 5.475 m²/person and the ACH 5 to 6 h^-1 is much since the occupant level is not a person per 2 m², the appropriate ACH is calculated and given below as:

(2 m²/person) ÷ (5.475 m²/person)× 5 h^-1 = 1.82 h^-1

Hence the actual ACH in the Chapel now is 0.95 h^-1 which is not correct.

Whereas the other AHU with 380 l/s does not supply the Chapel at all but it serves only Classroom 1 & 2, office 2 and Library. These zones have total area of 112.42 m² which means 3.8 l/s/m².

Assuming that the minimum ACH for all zones are 1.82 h^-1 based on the above calculation for the biggest zone in the church, the right airflow in the church is:

(6242.3 m³ ×1.8h^-1) ÷ 3.6 = 3121 l/s 3121÷1216 = 2.56 l/s/m²

To reduce the energy consumption, a VAV with a CO2 control system should be applied to all zones instead of a CAV system because the church activities do not run 24 hours a day, and the activities vary every day. Energy can be saved through ventilation losses and lower electricity consumption with a lower AHU heating demand.

5.1.2.2.1 Summary of the second retrofitting

This second retrofit is performed since the old AHU has been in operations for 4 decades.

The current heat exchanger has an efficiency of 50-60% and SFP 3-4 KW/m3/s, while the new chosen AHU with rotary heat exchanger has an efficiency between 70-80 % and SFP between 1.5-2 kWh/m³/s. Also, the first AHU with 1650 l/s airflow has a CAV system while the other starts manually or by timer according to the report in Appendix C.2 of Caverion company which made OVK (Obligatory ventilation control).

The current two AHU were replaced by a new one with a VAV system. It now has a total airflow of 2809/3121 l/s for air supplying and returning, respectively, which is equivalent to 2.31 l/(l/s.m²) and 2.56 l/s.m²). The pressure in the building is calculated with 10% under pressure, where it means that its supply is less than return air. With under pressure, moisture from the building cannot easily get out through floors, walls, and ceilings where there are air passages of some kind. This is important for ensuring the structural integrity of the

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building and also preventing mold, especially during the winter period when moisture in the building is at its peak.

The energy demand after changing the supply air to 2.31 l/s/m², return air to 2.56 l/s/m², and applying VAV system with CO2 Control. The calculation for heating demand is obtained to be 73 951.5 kWh/y. Thus, this result is much better than Retrofit 1 because the heat demand is reduced by about 43.5% compared to Retrofit 1, which has 130 790.1 kWh/y and 30 % to Base model. Also, that change reduced the max heat load from 59.03 KW to 35.49 KW. Heat demand presented is in table 14, while the new max heating load is represented in table 15.

Table 14. Heating demand in Retrofit_2

Heating demand Retrofit_2

Table 15. Heating load in Retrofit_2

Systems energy Retrofit_2

Retrofit_1 & Retrofit_2 model results comparison.

Table 16. Comfort Reference in Base and Retrofit_1

Results from table 16 above shows that there is difference after retrofitting due to changing of airflow and having VAV System.

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Figure 23 below presents the supplied energy between the Retrofit_1 & 2. The result shows Retrofit 2 has grand total 93 317 kWh/y while the Retrofit 1 has 13 8265 kWh/y. This means that the grand total of supplied energy for Retrofit_2 has significantly reduced by 36.5 %.

Figure 23. Supplied energy of Base and Retrofit_1

Furthermore, the energy system in zone heating has also reduced by 43% while AHU has 73% of heating reduction according to figure 24 presented below:

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Figure 24. Energy systems of Base and Retrofit_1

Another investigation was conducted on the Auxiliary energy after replacing AHUs with a new one containing a VAV system. However, the results obtained with auxiliary energy in figure 25 below show that fans in Retrofit_2 use 85% less energy than retrofit_1. Besides, the pumps have used lesser energy which is approximately 73%.

Figure 25. Auxiliary energy of Base and Retrofit_1

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In summary, the total heating and cooling for the building with the Retrofit_2 model show clearly that the most heating energy consumption takes place in December. The values for domestic hot water, ideal coolers and heaters, and the required AHU heating coil power AHU are demonstrated in figure 26 below.

Figure 26. Total heating and cooling

5.1.2.3 Retrofit 3

In Retrofit _3, all previous changes are kept. The only adjustment made is that the heating system is connected to district heating to determine the changes that would reduce energy computation. Energy system demand and max heating load in Retrofit_3 remain the same.

Table 17 below represent the heating demand in Retrofit_3 after simulation.

Table 17. Heating demand in Retrofit_3

Heating demand Base_Model kW/y

█ Zone Heating 34 559.9

█ AHU Heating 11 555.6

█ Dom.hot water 27 836

█ Total Heating 73 951.5

51 Retrofit_2 & 3 model results comparison.

Table 18: Comfort Reference

The change applied in Retrofit_3 gives the same results as in Retrofit_2 case as shown in table 18 above.

For supplied energy between the Retrofit_2 & 3, table 19 below shows that retrofit_3 has 139 019 KWh/y while the Retrofit_2 has 93 317 KWh/y. This means that the grand total of supplied energy for Retrofit_2 is 33% lesser than retrofit_3.

Table 19. Supplied energy of Base and Retrofit_1

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In Retrofit_3 used energy, which is presented in figure 27, the result remains the same after the comparison with the Retrofit_2. Therefore, the results of used energy, utilized free energy, Auxiliary energy, Energy for all zones during heating and cooling do not change as well. Results are shown in Appendix E.

Figure 27. Used energy for Base and Retrofit_1