ding with those determined by EVS 835: 2003, EN 806-3 and recorded values in school buildings.

to 2 times smaller than those calculated by the EVS standard and about 5 times smaller than those determined by the EN standard.

The big difference in DHW actual consumption and the same by standards due to the fact that standards are based on decades ago the situation. Thus, according to standards obtained the probability consumption does not meet the current situation.

Figure 6 shows the comparison of design flow rates determined for schools by the empiric formula, the standard EVS 835 and recorded values. It can be seen that in about 50% of schools the design flow rates determined by the empiric Formula (3) the flow rates are considerably smaller, in about 30% of the schools they are somewhat smaller and in 20% of the schools they are equal or somewhat bigger comparing with standard EVS 835.

At a same time the association with the actual design flow rates is better as the calculation depended on the

Figure 6. Comparison of the design flow rates determined for schools by the empiric Formula (3), the standard EVS 835 and recorded values.

number of water outlet devices only slightly, the majority of which are used marginally.

Variation graph of DHW consumption is presented in Figure 7. As can be seen in ordinary school there is no DHW consumption at weekend. Maximum consumption on weekdays takes place at lunchtime.

3.2. Kindergartens

The design flow rates recorded in kindergartens and those determined by the standard EVS 825:2003, and design flow rates calculated by Formula (4) are presented in Table 3.

In Table 3, we can see that the design flow rates determined by EVS 835: 2003 are bigger than the actual ones, which fact results in over dimensioning the DHW instantaneous heat exchangers and the control devices.

As the design flow rates determined by the EVS standard are up to 1.8 times bigger than the measured ones in kindergartens, a new empirical formula is presented for determining them in selecting water heating devices (4)

(4)

where q—design flow rate l/s; N1 is the number of showers, N2 is the number of children, N3 is number of water outlet devises.

Table 3 shows that the design flow rates determined by Formula (4) are up to 1.7 times smaller than the ones determined by the EVS standard.

Variability graph of DHW consumption in kindergarten is presented in Figure 8. Maximum consumption in kindergartens can take place in the morning, at lunch time as well as in the afternoon. On most days the top maximum consumption occurs at lunchtime.

3.3. Office Buildings

Table 4 presents the design flow rates recorded in office buildings and those determined by EVS 835: 2003,  

Figure 7. Weekly variability graph of DHW consumption in the educational building.

Figure 8. Weekly variability graph of DHW consumption in kindergarten.

Table 3. Comparison of the design flow rates determined by the results of recording with those determined by EVS 835: 2003 and Formula (4).

Table 4. Comparison of the design flow rates determined by the results of recording with those determined by EVS 835:2003 and EN 806-3 in office buildings.

EN 806-3 and building parameters. A comparison of these standards values with the results of recording is given in Table 4

A new empirical Formula (5) for determining the design flow rates in dimensioning the water heating devices was recommended

(5)

where q—design flow rate l/s; N1—number of showers; N2—number of people; N3—number of water outlet devises.

Table 4 shows that the use of EVS 835: 2003 leads to a most considerable over dimensioning of the DHW instantaneous heat exchangers and the control devices. In Table 4, it can be seen that the design flow rates of office buildings determined by the Euro standard are not suitable for Estonia, because the results obtained are more than 10 times bigger than the measured consumption in office buildings. The reason is that the probability consumption does not meet the current situation.

Table 4 shows that the design flow rates in office buildings determined by the standard EVS 835 are about 4 and even more times bigger than the maximum flow rates measured. The results obtained by determining the flow rates by the Euro standard are even up to 15 times bigger than the maximum flow rates measured. For that reason a new empiric formula has been worked out for determining the design flow rates for office and public buildings (5).

Table 4 shows that the design flow rates determined by Formula (5) are up to 2 times smaller than those determined by the standard EVS and up to 8 times smaller than the design flow rates determined by the Euro standard.

Figure 9 presents a comparison of the design flow rates determined for office buildings by the empiric Formula (5), the standard EVS 835 and recorded values. We can see that design flow rates determined by the Formula

Figure 9. Comparison of the design flow rates determined for office buildings by the empiric formula (5), the standard EVS 835 and recorded values.

(5) are more close to recorded values. 

The weekly variability graph of DHW consumption in the office building is presented in Figure 10. The graph given in Figure 10 is typical of smaller office buildings that have no sauna. Characteristic of such office buildings is the DHW consumption only on workdays with the top consumption only at lunchtime.

3.4. Shopping Centers

Table 5 gives a comparison of the recorded maximum flow rates, design flow rates determined by the standard EVS 835 and the Formula (6) and the values that affect the water consumption.

Table 5 shows that the DHW design flow rates determined for trade centers by the standard EVS 835 are at least 3 times bigger than the actual maximum consumption. Such a situation made it necessary to work out a new calculation formula for determining the DHW design flow rates for trade centers.

One of the reasons for the great difference between the actual DHW maximum consumption and the design flow rates determined by the standard EVS is the fact that the preparation of semi-fabricated food on the spot has been finished. 

Below we present a recommendable calculation Formula (6)

(6)

Where q is design flow rate l/s; N1 is number of showers; N2 is number of visitors; N3 is number of water outlets.

4. Conclusions

With drastically decreased DHW consumption rising a need for new calculation formulas for determining the DHW design flow rates for instantaneous heat exchangers, the new calculation methodology of dimensioning

Figure 10. Weekly variability graph of DHW consumption in office building.

Table 5. Comparison of the recorded maximum flow rates, design flow rates determined by the standard EVS 835 and the formula (6).

instantaneous heat exchangers for DHW systems is of particular importance. In the papers of several investigators, it has also been pointed out that for heating DHW it would be suitable to use instantaneous heat exchangers instead of tank type water heaters. This would at the same time decrease the risk of Legionella disease.

The DHW design flow rates determined for office buildings and shopping centers by the recommended empiric formulas are about two times lower than those determined by the still used method EVS 835. 

5. Acknowledgements

Publication of this article was supported by the ESF measure 1.2.4, Development of cooperation and innovation of universities, the sub-measure “Doctoral Schools” that finances the project “Construction and Environmental Engineering PhD School”—project code 1.2.0401.09-0080. 

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