4.3.1 Building sample
The valorisation of the above resources by way of HP systems will be tested on the same multi-family building sample which was used in Chapter 3:
2 new buildings with identical low energy SH demand, but differentiated DHW demand.
3 retrofitted buildings, of which one with low SH and the other ones with intermediate SH demand and dif-ferentiated SH distribution temperature.
1 non retrofitted building
The main characteristics of the building sample (SH demand corresponding to standard weather data) are summarized in Table 4:4. Note that 4 of the buildings correspond to actual case studies situated in Geneva (New, Retrofit best case, Retrofit reference, No-retrofit), while the 2 other ones are combinations thereof, in terms of DHW demand (New low DHW) or of SH distribution temperature (Retrofit intermediate).
Accronym Case study Qsh Qdhw Qdem Tsh.0
kWh/m2 kWh/m2 kWh/m2 °C
New (1) SolarCity 20.8 47.7 68.5 30
New low DHW (1’) SolarCity, adapted 20.8 28.3 49.1 30
Retrofit best case (2) Cigale 37.8 34.6 72.4 40
Retrofit intermediate (3’) Gros Chêne, adapted 69.3 28.3 97.6 40 Retrofit reference (3) Gros Chêne, build. A 69.3 28.3 97.6 50 No-retrofit (4) Gros Chêne, build. B 110.0 28.3 138.3 50
Table 4:4 Main characteristics of the building sample (with climatic correction of SH demand to standard weather data).
Qdhw, Qsh, Qdem: DHW, SH and total annual heat demand (with climatic correction to standard weather).
Tsh.0: SH distribution temperature, at 0° outdoor temperature.
Case studies: (1) SolarCity (Fraga et al., 2015); (2) Cigale (Tornare et al., 2016); (3-4) Gros-Chêne, building A and B (Mermoud et al., 2012).
4.3.2 Benchmarking with the multifamily building stock of Geneva
In order to assess its representativeness, the chosen building sample is hereby compared to the 19.3 million m2 of the multifamily building stock of the canton of Geneva.
Firstly, in Table 4:5, statistic values are presented for the heat demand (SH + DHW) of the 19.3 million m2 (Khoury, 2014). These values are based on Geneva’s building stock in 2010, with correction of SH demand to standard weather data.
Qdem Qdem
MJ/m2 kWh/m2 1st decile (10%) 316 88 1st quartile (25%) 367 102
Median (50%) 416 116
3rd quartile (75%) 465 129 9th decile (90%) 526 146
Average 415 115
Table 4:5 Heat demand (SH + DHW) statistics of the 19.3 million m2 multi-family building stock of Geneva (source: Khoury, 2014).
Potential and constraints of available heat sources in relation to various building demands.
Considering our building sample (Table 4:4), all except No-retrofit are in the 1st quartile, with New, New low DHW and Retrofit best case being in the 1st decile. No-retrofit is in the opposite side of the scale as it is in the 4th quartile. The average heat demand of the MF building stock of Geneva (115 kWh/m2) is between Retrofit reference/intermediate and No-retrofit.
Secondly, comparison in terms of SH demand only is presented in Figure 4:4. This figure shows the distribution of the SH demand of the MF building stock in Geneva, grouped according to the three major construction periods. It is the result of a detailed survey using the Geneva SITG database, which contains the measured final energy consumption for heating (SH and DHW) as well as the associated heated area of the multi-family residential buildings of the Canton (Khoury, 2014). In the figure, our chosen building sample is represented by the red dots.
Figure 4:4 Benchmarking with the SH demand of the multi-family building stock of Geneva (source: Khoury, 2014).
As shown in the figure, New (and New low DHW), Retrofit best case and Retrofit reference (Retrofit intermediate) are in the 1st decile, meaning that they are representative of the best cases in their respective construction periods. No-retrofit is in the 3rd quartile, close to the 4th quartile, meaning that it is representative of lower than average building envelopes. Also, in our building sample, only New (and New low DHW) are close to the SH demand standards SIA and Minergie-P retrofit. All other buildings from our sample, as well as the majority of Geneva building stock, are way above.
Potential and constraints of available heat sources in relation to various building demands.
Thirdly and lastly, comparison in terms of DHW demand is presented in Figure 4:5. This figure shows the heat con-sumption for DHW demand (including storage and distribution heat losses, Qdhw.is) of 434 multifamily buildings in Ge-neva (approximately 1 million m2 of heated surface). It is the result of a comparative study on heat consumption for DHW in which monthly heat consumption data from 61 district heating substations was analysed (Quiquerez et al., 2017). In the figure, the building samples of this study are represented in numbered red dots. Note that the red dots values are around 10% higher than the values in Table 4:4 because they include storage losses, in order to be compa-rable with the data from the so mentioned study (Quiquerez et al., 2017).
Figure 4:5 Benchmarking with the heat for DHW demand of the multi-family building stock of Geneva (source: Quiquerez et al., 2017).
Inversely to SH demand, when heat for DHW demand is concerned, New is in the 4th quartile, amongst the highest values of the figure. Retrofit best case is slightly above the median and all other samples (that by definition have the same DHW demand) are in the 2nd quartile, closer to the 1st quartile than to the median.
The SIA limit (20.8 kWh/m2 of DHW heat delivered to the end consumer) is way below the values of the benchmark, but does not include storage nor distribution losses. However, even assuming that these losses would amount to 20%, the SIA equivalent heat consumption for DHW demand would only amount to 25 kWh/m2, i.e. within the 1st decile.
4.3.3 Rescaling of annual and hourly heat demand
In this section, building demand is rescaled for 2010, the common reference meteorological year chosen for the heat sources. For the rescaling, we consider that:
DHW demand is independent of the meteorological year and is therefore the same as for standard weather data
SH demand is rescaled according to 2010 degree days (2048 K.day over the Oct-Apr period, on a 18/12 °C ba-sis) as opposed to the standard weathers (2385 K.day).
The 2010 SH and DHW demands, as well as SH distribution temperatures, are represented in Figure 4:6 (annual val-ues) for all 6 building types.
0 10 20 30 40 50 60
0 10 20 30 40 50 60
Q
dhw,is[kWh /m
2/yr ]
Substations
● Qdhw,is(3rdquartile, median and 1st quartile) 1) New (SolarCity) 1’) New low DHW 2) Retrofit best case (Cigale) 3’) Retrofit intermediate 3) Retrofit reference (Gros-Chêne) 4) No-retrofit (Gros-Chêne)
SIA lim
1)
2) 3), 4), 1’) & 3’)
Potential and constraints of available heat sources in relation to various building demands.
Figure 4:6 Space heating (SH) and domestic hot water (DHW) demand of the building sample (adjusted to 2010 weather data) as well as SH distribu-tion temperature at 0°C outdoor temperature (dots, right axis).
When comparing the building demands between standard weather and 2010, we observe that the decrease of SH demand (equivalent to the decrease in the overall demand) is minor for New, New low DHW and Retrofit best case (3.0, 3.0 and 5.3 kWh/m2 respectively) but it becomes important for Retrofit intermediate, Retrofit reference (9.8 kWh/m2) and for No-retrofit (15.6 kWh/m2). This SH decrease leads to an increase of DHW share of less than 4%. This small impact is explained by the fact that important decrease of SH occur for building types with lower DHW shares.
Overall, the demand structure remains quite similar to the standard weather demand.
Similarly to Chapter 3 section 3.3.3, the hourly demand profile is defined as follows:
For DHW, the hourly profile is given by the monitored data of a typical multifamily building (Zgraggen, 2010).
The profile is adjusted by a multiplication factor, so that the integral of the load corresponds to the annual DHW demand of the building under consideration.
For SH, the hourly load is given by a linear function of the outdoor temperature, and is defined by a set point above which SH is off and by a nominal heat load at 0°C outdoor temperature. The nominal heat load at 0°C is adjusted so that the integral of the load corresponds to the annual SH demand of the building under consid-eration and for the considered meteorological year.
For SH distribution temperature, it is given by a linear function of the outdoor temperature, adjusted to the building typology (see Table 4:6, section 4.4.2). The DHW distribution temperature is considered constant, at 55°C.
The yearly dynamic, for all 6 building types, is presented in Figure 4:7 in daily values.
0
Potential and constraints of available heat sources in relation to various building demands.