Heat recovery potential of domestic grey water in the pilot project Jenfelder Au in Hamburg
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th
17 EWA Symposium during IFAT 2014, Munich, Germany, 5-9 May 2014
Water, Energy and Resources: Innovative Options and Sustainable Solutions
Session 4: Energy and Resources in New Sanitation Approaches – Part Two
Heat recovery potential of domestic grey water
in the pilot project Jenfelder Au in Hamburg
Jan Sievers1, Jörg Londong1, Andrea Stübler2, Dominik Bestenlehner2,3,
Harald Drück2,3, Wenke Schönfelder4
1
Bauhaus-Universität Weimar
Coudraystraße 7, 99423 Weimar, Germany
2
Solar- und Wärmetechnik Stuttgart (SWT)
Pfaffenwaldring 6, 70550 Stuttgart, Germany
3
Institute of Thermodynamics and Thermal Engineering (ITW)
Research and Testing Centre for Solar Thermal Systems (TZS)
University of Stuttgart, Pfaffenwaldring 6, 70550 Stuttgart, Germany
4
Hamburg Wasser
Billhorner Deich 2, 20539 Hamburg, Germany
Keywords: new sanitation systems, grey water, heat recovery, hot water preparation, district,
Jenfelder Au
Abstract
In Hamburg (Germany) a new urban district with approximately 2,000 inhabitants - the Jen-
felder Au - is being developed. As part of a demonstration project the so-called HAMBURG
WATER Cycle® (HWC) will be implemented there. The HWC establishes synergies between
wastewater management, waste management and energy production and is based on the
separated collection of wastewater streams from households. The objective of this article is
to elaborate the possibilities of using the thermal energy content of the grey water flow and to
estimate the primary energy saving potential by using grey water heat recovery systems. In a
first step, typical values for the temperature and flow rate of grey water will be presented.
Afterwards, various types of residential grey water heat recovery systems will be introduced
and their advantages and disadvantages will be compared. Using typical values for the tem-
perature and flow rate of the grey water selected systems (local and centralised ones) will be
implemented into the transient energy system simulation software TRNSYS version 17
page 1/20
[Transsolar Energietechnik GmbH] and a simulation study will be carried out. The results of
the dynamic system simulations for the different systems will be compared with regard to
their thermal performance and the primary energy savings obtained by heat recovery.
1. Introduction
A new urban district for approximately 2,000 inhabitants - the Jenfelder Au - is being devel-
oped in Hamburg Wandsbek (Germany). As a demonstration project the so-called
HAMBURG WATER Cycle® (HWC) – an innovative, integrated wastewater and energy pro-
duction concept – will be implemented there. The HWC is based on the separated collection,
drainage and on site treatment of wastewater streams from households. The wastewater will
be collected in a 2-material-flow system – blackwater and grey water [DWA, 2013]. The con-
centrated blackwater will be collected by a vacuum sewer system and fermented together
with organic waste. The produced biogas will be used to operate two micro gas turbines and
cover partly the heating and electricity demand of the buildings within the district Jenfelder
Au. Within the framework of the German research project KREIS (Kopplung von regenera-
tiver Energiegewinnung mit innovativer Stadtentwässerung / Linking sustainable energy gen-
eration to innovative urban drainage), concepts and methods for energy supply and
wastewater disposal for districts are developed and researched. The article on hand shows
the possibilities and potentials of using the thermal energy content of the grey water flow in
the district.
Grey water is defined as wastewater from baths, showers, washing machines as well as
dishwashers and kitchen sinks, excluding wastewater from toilets [DIN 4045:2003; Birks et
al. 2007; EN 12056-1:2001, Jefferson et al. 2004]. Wastewater from bathrooms, showers
and baths is referred as light grey water [Friedler et al. 2006, Birks et al. 2007, Chaillou
2010]. Grey water that additionally includes more polluted wastewater from washing ma-
chines, dishwashers or kitchen sinks is called dark grey water [Birks and Hills 2007]. Grey
water is the largest domestic wastewater flow with about 60 to 75 % of the total wastewater
flow [Eriksson 2002, Friedler 2004]. The energy associated with producing domestic hot wa-
ter (DHW) represents a significant share of the total energy consumption of a typical house-
hold [Eslami-Nejad et al. 2009]. Approximately 14 % of the total final energy consumption of
households in the year 2010 in Germany is related to the domestic hot water preparation
[AGEB 2013]. Most of the energy, which was originally used to prepare domestic hot water,
is drained into the sewerage with the grey water. Used hot water still contains 80 to 90 % of
the thermal energy related to the necessary energy to prepare the DHW [Cooperman et al.
2011]. Grey water heat recovery systems (GWHR) can be used to recover partly this thermal
energy.
The article provides an overview about grey water heat recovery systems. Different systems
will be discussed with regard to the possibility of an implementation into the district Jenfelder
Au. Various types of residential grey water heat recovery systems will be taken into account
and their advantages and disadvantages are compared. Using typical values of temperature
and flow rate of grey water flows, selected systems will be implemented into the transient
system simulation software TRNSYS version 17 and a simulation study will be carried out.
The results of the dynamic system simulations for the different systems will be compared
with regard to the effective usable heat recovery.
page 2/20
2. Flow rates and temperatures of grey water
Flow rates of grey water
Grey water is the largest domestic wastewater flow with about 60 - 75 % of the total
wastewater flow [Eriksson 2002, Friedler 2004]. In Germany about 60 - 90 Liter per capita
and day (l/(c∙d)) of grey water is drained into the sewerage [DWA 2013, Rosenwinkel 2004,
fbr 2005, Otterpohl 1999]. Based on data of the average drinking water consumption an av-
erage grey water quantity of about 72 l/(c∙d) can be estimated [DVGW 410:2004, BDEW
2012]. Due to a literature review of Meinzinger et al. (2009) the median-value of grey water
flow in central Europe is 110 l/(c∙d). Zeeman et al. (2008) found for two sites in the Nether-
lands volume flows of 60 – 70 l/(c∙d) respectively 90 l/(c∙d). In the literature study of Keysers
et al. (2008) average grey water flows of 75 l/(c∙d) are given. Knerr et al. (2009) found an
average grey water flow of about 79 l/(c∙d) for a multi-family house in Kaiserslautern, Germa-
ny. The evaluation of operating data of the settlement Flintenbreite in Lübeck, Germany,
showed an average grey water flow of 61 l/(c∙d) [Oldenburg et al. 2008].
Due to the high uncertainty of results, which is even more problematic looking at grey water
concentration and load measurements [Sievers et al. 2014], initial studies were carried out by
a team of the Bauhaus-Universität Weimar. Related to a multi-story building in Berlin (Ger-
many) with 20 apartments and 51 residents, temperature and flow rates of grey water were
measured for a period of 17 days in November 2012 and April 2013. The measuring point
was located in an infrastructure room within the building. The measurement was performed
with a sampling device for volume-proportional sampling of grey water and was done using
probes, which logged the temperature in a one-minute interval. The average grey water flow
was about 3,900 l/(c∙d) (± 800 l/c∙d)) or 77 l/(c∙d) (± 15.7 l/(c∙d)). The diurnal pattern of the
grey water flow is shown in figure 1.
Temperature levels of grey water
In the public sewer system the wastewater temperature is about 10 – 15 °C throughout the
year with peaks of up to 20 °C during the summer. Temperatures of domestic wastewater or
grey water in the buildings are significantly higher [DWA 2010, Koppe et al. 1999]. For
wastewater inside buildings temperatures of about 16 – 23 °C are published by Wanner
(2009) and van Velsen et al. (2013). A measurement-based analysis of the energetic poten-
tial of wastewater within four buildings in Germany of Brunk et al. (2012) showed tempera-
tures between 23 – 25 °C. The study by Heinz et al. (2013) shows wastewater temperatures
between 16 – 38 °C for a detached house with grey water treatment and a multistory building
with conventional drainage system.
The temperature range for grey water given in the literature reviews of Morel & Diener (2006)
and Eriksson et al. (2002) indicates temperatures of 18 – 30 °C respectively 18 – 38 °C. Li et
al. (2008) found average temperatures of 20 °C (± 0.3 K) for the influent of a grey water sep-
tic tank in the ecological settlement Lübeck Flintenbreite, Germany [Li et al. 2008]. Knerr et
al. (2009) indicates a temperature range of 14.6 – 43 °C for a residential building with eight
flats and 15 residents in Kaiserslautern, Germany. The mean value of the dark grey water
page 3/20
was determined to 29.4 °C. In the report of Menger Krug et al. (2010) average temperatures
of 30 °C of light grey water are given for a dormitory with 65 students in Freiburg, Germany.
The studies by Bauhaus-Universität Weimar performed in Berlin showed grey water tempera-
tures well above 20 °C. The calculation of the mean value of the grey water temperature ef-
fluent has been carried out by a quantitative weighting with the simultaneously measured
one-minute flow rate and is given in °C. During the measurement campaigns the average
flow-weighted grey water temperature could be determined to 22.6 °C. Minimum and maxi-
mum daily flow-weighted temperatures are between 21.1 °C and 24.6 °C. The temperature
data show a similar pattern as the grey water flow. In general higher temperatures are ob-
served during times of high grey water flows and low temperatures when the grey water
flows are low. In summary, it can be noted that the diurnal variation shows a pronounced
grey water flow peak in the morning and a second weaker peak in the evening. The diurnal
variation in temperature and grey water volumes is given in figure 1. The flow is shown as a
bar chart and the corresponding average grey water temperature as a line graph.
Figure 1: Diurnal variation in temperature and grey water flow in April 2013
3. Local options of heat recovery in the Jenfelder Au
Basically three locations are possible for the heat recovery systems from wastewater. As
shown in figure 2 heat can be recovered at the source in the building, in the sewer or at the
treatment plant [Müller 2009].
page 4/20
Heat recovery in buildings Heat recovery in the sewer Heat recovery at sewage treatment plants
Figure 2: Possible locations for wastewater heat recovery systems [Müller et al. 2009 (modified)].
A heat recovery potential also exists “local” near the valves and taps in the building, or in the
basement before the wastewater is leaving the house. The household devices, which can
supply grey water to the heat exchanger, are limited to showers, bathtubs, washing ma-
chines and dishwashers. These appliances usually use only warm water. Other devices like
kitchen sinks and washing basins supply cold water as well as warm water to the grey water
system. The grey water flow has a high variability both in quantity and quality of effluents
[Friedler 2004, Eriksson et al. 2002]. Basically there are two generally different systems of
local wastewater heat recovery systems: On-demand heat exchangers and heat exchangers
combined with stores.
With local on-demand heat exchangers, the thermal energy of the warm wastewater is direct-
ly used to preheat cold drinking water and thus to reduce the required heating demand. Es-
sentially, there are two basic types of local on-demand heat exchangers. Horizontal heat ex-
changer units which are integrated in the shower tray, or so-called Gravity Film Heat Ex-
changer (GFX-Units) that take advantage of the drain water film flowing down the inner walls
of the vertical pipe. On-demand heat exchangers can be used wherever wastewater and
freshwater is flowing simultaneously [van Velsen et al. 2013]. If the heat exchanger is sub-
merged in a store, heat recovery and wastewater drainage can be decoupled. [van Velsen et
al. 2013, Nolde 2013]. Store based local heat exchangers use the heat of the entire grey wa-
ter to preheat freshwater. [van Velsen et al. 2013, CCHT 2007]. To avoid a contact between
the two media and for optimal utilization of the heat recovery potential it is possible to inter-
pose a buffer heat store with an additional heat exchanger and preheat the freshwater
through a second heat exchanger [Nolde 2013, Nolde 2014]. Possible installation alterna-
tives for local heat exchangers are shown in figure 3.
page 5/20
(A) (B)
Figure 3: Installation schemes for local heat exchanger (A): Local on-demand heat exchanger.
(B): store heat exchanger [Meander heat recovery, 2014 (modified)]
Three basic technologies are commonly used to install local on-demand heat exchanger us-
ing either balanced or unbalanced flows (figure 4) [Coopermann et al. 2011, DOE 2005]. In
balanced flow configuration, the preheated water feeds the water heater inlet as well as the
cold water inlet of the shower. Thus, all of the cold water, necessary for shower, passes the
local heat exchanger before the splitting to the water heater. This arrangement ensures that
the incoming water is balanced by an equal flow of drainwater [Coopermann et al. 2011,
DOE 2005]. In unbalanced flow configurations the cold water site of the shower’s mixing
valve is either preheated by a local heat exchanger or the preheated water flows to the water
heater. In this case the flow rate of the drainwater flowing through the heat exchanger is
higher than the flow rate of the preheated water. This flow imbalance causes a larger tem-
perature rise in the freshwater than the temperature drop in the drainwater. This is the rea-
son why balanced flow installations are more efficient than unbalanced flow configurations
[Coopermann et al. 2011, DOE 2005]. Possible installation schemes for localized horizontal
on-demand heat recovery systems are presented in figure 4.
(A) (B) (C)
Figure 4: Installation schemes for local heat exchanger. (A): Balanced flow; (B): unbalanced flow cold
water preheat; (C): unbalanced flow- warm water preheat [Meander heat recovery 2014 (modified)]
page 6/20Local on-demand heat exchangers can recover heat only under continuous flow conditions.
About 50 – 60 % of the total grey water flow accounts to light grey water from showers or
baths [Ramon et al. 2004]. According to Chaillou et al. (2010) about 40 – 50 % of grey water
quantity is washing water from shower and bath [Chaillou et al. 2010]. In Germany about
43 l/(c∙d) are used for bodycare (bathing, showering), which correspondents to about 60 % of
the daily grey water flow of 72 l/(c∙d) [BDEW 2012, DVGW 2004]. Foekema et al. (2011) give
consumptions per resident of 48.6 l/d for showering and 2.8 l/d for bathing for the Nether-
lands. The average time for showering takes about 8.1 minutes [Foekema 2011]. The litera-
ture reviewed by Neunteufel et al. (2010) gives an average per resident of 47 l/d and a medi-
an of 45 l/d for the European Union. The minimum water consumption for showering is
32 l/(c∙d), the maximum is 90 l/(c∙d) [Neunteufel et al. 2010]. A recent study of Neunteufel et
al. (2012) gives a water consumption for Austria of 36 Liter per usage and an average fre-
quency of use of 0.7 utilizations per resident and day.
Almeida et al. (1999) presented a mean value of 42.3 Liter for each shower process with a
range of 32 – 95 Liter. The temperature level in light grey water is usually higher than in dark
grey water. At the shower head the temperatures are about 38 °C [Brunk et al. 2012] [Rob-
ert 2014]. In the shower tray the temperatures are in a range of 30 – 33 °C [Robert 2014].
Blom et al. (2010) give temperatures of about 35 °C for the effluent of the shower. These
values fit well with the data of Wong et al. (2010), who found a temperature drop from the
shower head to the shower drain of about 2 – 6 K.
Selection of local heat recovery systems to be investigated
The results shown in chapter 7 of this article are for the local heat recovery systems based
on horizontal heat exchangers below the shower tray which are installed in balanced or un-
balanced flow configuration. The heat exchangers are used for preheating cold water (figure
4, configuration A and B). The reasons for this decision are a relative ease of installation and
the option to install the systems during retrofitting. Further advantages of these systems are
that the water in the shower drain has high temperatures of about 32 °C and a short distance
between heat source and heat demand. Due to the short pipe lengths and the small tempera-
ture difference between the preheated water and the ambient temperature it can also be as-
sumed that the heat losses are very low.
4. Central options of heat recovery in the Jenfelder Au
The entire grey water of the urban district Jenfelder Au will be collected using gravity sewers
towards the grey water pumping station located at the West-North end of the urban district.
From there the grey water will be pumped to the work yard via the approximately 440 m long
pressure sewer. Currently the type of grey water treatment technology is subject to investi-
gate in the KREIS research project. Once the technology is decided, a grey water store will
be built at the work yard that feeds the grey water treatment plant. An Overview of the district
Jenfelder Au is shown in figure 5.
page 7/20Greywater
pumping station
Greywater
pressure sewer
Figure 5: HAMBURG WATER Cycle® in the urban district Jenfelder Au
As “central” heat recovery system, meaning the recovery within the grey water sewerage
system of HAMBURG WATER or the recovery at the work yard close to the grey water treat-
ment plant the following options seem feasible for the Jenfelder Au:
1) It is theoretically possible to install a double pipe counterflow heat exchanger in sections of
the sewer pipes that direct towards the grey water pumping station on the Western and on
the Eastern edge of the water storage area. These are the pipe sections with the highest
flow rate within the grey water system in the Jenfelder Au. But in these pipe sections,
abundant house connections are located, so it is practically too complicated to install an
insulated double pipe heat exchanger there.
2) A second option is the pit of the grey water pumping station with a depth of approximately
8.60 m. This installation location beneath the pumps is not very practical because space is
limited and essentials like cleaning and maintenance under the pumps are impeding this
option. Another adverse aspect is that the inflow and outflow is discontinuous; it is ex-
pected that the pump works 4 times per hour for approximately 5 minutes.
3) The approximately 440 m long pressure sewer from the grey water pumping station to the
grey water store at the work yard would be suitable for heat recovery. This sewer is per-
manently filled as it rises on the way to the work yard because of level differences of ap-
proximately 4.5 m. There are no house connections on this pressure sewer. It is possible
and seems reasonable to install a double pipe counterflow heat exchanger in this pressure
page 8/20sewer. But as this sewer has already been built it is practically not a feasible solution.
Therefore the fourth option is being considered.
4) When the decision to build a specific grey water treatment plant has been made, a grey
water store with a volume of approximately 80 m3 will be needed. The grey water is
pumped from the pumping station via the pressure sewer to this store located at the work
yard. From there the treatment plant will be supplied with grey water continuously. The
store seems the most suitable and implementable location for the installation of a heat re-
covery system as the store needs to be built in any case and the lower part of the store will
be filled with grey water at any time. As this fourth option is the most feasible that could be
implemented, it will be further investigated as the central system in this article.
5. Description of the investigated systems and boundary conditions
In this study, three grey water heat recovery systems are considered and investigated related
to their thermal performance, among them two local systems and one central system. The
district which will be connected to the HWC and which is investigated in this study consists of
610 accommodation units (AU), each occupied by three residents. The selected systems, im-
plemented in the simulation model, are described as followed.
Central System
The total grey water flow of the buildings is drained to the pumping station by a gravity sew-
er. By reaching the maximum filling volume (6 m³), the pumping process starts and conse-
quently the grey water is transported by a pressure sewer to the grey water store at the work
yard. The grey water is extracted from the grey water store within a continuous process and
is purified by subsequent steps.
The purification steps of the grey water flow need to be carried out by a minimum tempera-
ture of 10 °C, that’s why the temperature difference between the output of the grey water
store and 10 °C are considered as heat recovery potential. As the temperature of the grey
water at the work yard is too low in order to realize a centralised direct use of the heat e.g.
for space heating or domestic hot water preparation, a heat pump is necessary and imple-
mented in the consideration. Figure 6 shows the way of the grey water between the locations
of the buildings and the work yard. Relevant parameters and boundary conditions are listed
in table 1.
Figure 6: Schema of the central system
page 9/20Table 1: Parameters and boundary conditions of the central systems
gravity sewer
1
average length between building and pumping station 559 m
1
nominal diameter DN 200
1
wall material and thickness polypropylene (7.7 mm)
pumping station (soil-buried)
1
maximum filling volume of the pumping station 6 m³
1
wall material and thickness ferroconcrete (22 cm)
pressure sewer
length 436 m
nominal diameter DN 125
wall material and thickness polyethylene (4 mm)
laying depth 1.35 m
grey water store (soil-burried)
volume ~ 80 m³
wall material and thickness ferroconcrete (22 cm)
1
[Zündorf et al. 2012]
Grey water data used for central system
For implementing a realistic data base for the accumulating grey water of the residents,
measured data of the Bauhaus-Universität Weimar related to a multi-story building in Berlin
with 20 apartments and 51 residents were used (see chapter 2). The measured values for
temperature and flow rate during the course of a day were averaged over a period of 10 days
and scaled up linearly to a district size comprising 1,830 residents. The resulting values used
for this study are shown in figure 7. The total volume of grey water per resident is about
75 Liter per day and the temperature is mostly in the range between 20 and 30 °C.
page 10/20Figure 7: Flow rate and temperature of the total grey water for a typical day of the district
Local systems (A and B)
In this investigation, two local shower tray heat recovery systems (A and B) are considered.
By means of these systems the grey water from the shower is chilled by preheating the cold
water flow via a heat exchanger. Consequently, only the part of the grey water generated in
the shower tray can be used for heat recovery. The two different systems (A and B) are
shown in the figures 8 and 9. The local system A (figure 8) is characterized by the fact that
only a part of the cold water flow used for the shower can be used for preheating. The other
part of the cold water flow is directly heated up by the water heater. This installation option
offers the possibility of an easy integration into existing or newly built buildings direct under
the shower tray and without any special components. However, it should be taken into ac-
count, that the heat recovery potential is limited and depends besides the heat exchanger
efficiency, also on the heat source temperature.
page 11/20Figure 8: Schema of the local system A (unbalanced flow)
The local system B is shown in figure 9. Compared to the local system A, the whole cold wa-
ter flow of the shower is preheated by the grey water flow. This leads to a higher heat recov-
ery but usually also to a higher installation effort. Either a water heater at the location of the
shower, or long pipelines from the shower to the water heater and back to the shower are
necessary in order to realize this option. The implemented parameters and boundary condi-
tions of the two local systems are listed in table 2.
Figure 9: Schema of the local System B (balanced flow)
Table 2: Parameters and boundary conditions of the local systems (A and B)
number of showers per resident and day 1
volume of water per shower 32 Liter
Temperatures
cold water 10 °C
hot water from heat source 60 °C
shower 38 °C
grey water from shower 32 °C
page 12/206. Investigation methods
In order to compare the different heat recovery systems related to their thermal behavior and
especially to their heat recovery performance, the transient system simulation software
TRNSYS in version 17 is used. In a first step, all relevant components of the different sys-
tems influencing the thermal behavior, and the ground temperature of Hamburg in order to
determine the heat losses of the components (e.g. of the pipes), are implemented into the
simulation model. Afterwards simulations of the dynamic behavior of the three systems were
carried out over a period of one year, with a time step of 90 s. The results of these simula-
tions are compared to each other, regarding the heat recovery performance. A further com-
parison between the three systems is performed based on the respective primary energy
saving, assuming that the recovered heat substitutes the consumption of natural gas.
7. Results
The heat recovery performance of the different grey water heat recovery systems is shown in
table 3. The table contains both, the annual recovered heat and the percentage of the recov-
ered heat related to the total heat amount of the grey water. The total heat amount of the
grey water is defined by the heat amount based on a reference temperature of 10 °C.
Table 3: Annual recovered heat and percentage of the recovered heat according to the different grey
water heat recovery systems
Central system Local system A Local system B
Recovered heat [MWh/a] 545 196 328
Percentage of the recovered heat related to 69 25 41
the total heat amount of the grey water [%]
(related to a temperature of 10 °C)
According to these results, the total recovered heat of the district is 545 MWh/a for the cen-
tral system, which is equal to 69 % of the heat amount in the grey water, related to a temper-
ature of 10 °C. For the local system A the heat recovered is 196 MWh/a corresponding to
25 % of the heat amount in grey water and for local system B 328 MWh/a corresponding to
41 % of the heat amount in grey water. Figure 10 shows monthly values of the recovered
heat of the different systems.
page 13/20Figure 10: Grey water heat recovery potential of the district, related to the different systems
Consequently, the heat recovery potential of the central system is the largest although high
heat losses during the transport between building and work yard occur. Regarding the local
systems heat losses are insignificant, but the fact that only a part of the grey water flow rate
can be used for heat recovery is a disadvantage. The comparison of the recovered heat
doesn’t consider the fact that for the central system, a heat pump is necessary.
In order to qualify the ecological impact of the different grey water heat recovery systems, an
assessment based on the primary energy saving for each system was performed additional-
ly. For this assessment two different sets of primary energy factors have been used. Since
the district “Jenfelder Au” is located in Germany, the primary energy factors of the current
German regulation “Energieeinsparverordnung 2014” (EnEV 2014) are used. Additionally,
the primary energy factors of the European standard EN 15603 are taken into account.
With regard to this consideration it is assumed that the heat recovered from the grey water,
replaces the consumption of natural gas. Table 4 shows the two sets of primary energy fac-
tors for both, electricity and natural gas.
Table 4: Used primary energy factors [EnEV 2014, EN 15603:2008]
Electricity Natural gas
EnEV 2014 2.0 1.1
EN 15603 3.14 1.36
page 14/20The annual primary energy savings of the different investigated systems are shown for the
two sets of primary energy factors in table 5:
Table 5: Annual primary energy saving of the different investigated systems
Central system [MWh/a] Local system A [MWh/a] Local system B [MWh/a]
EnEV 2014 403 216 361
EN 15603 353 267 447
The figures 11 and 12 show the monthly values of the primary energy savings for the differ-
ent investigated systems for the two sets of primary energy factors.
Figure 11: Primary energy savings for the different systems, calculated with primary energy factors
according to EnEV 2014 (electricity: 2.0; natural gas: 1.1)
page 15/20Figure 12: Primary energy savings for the different systems, calculated with primary energy factors
according toEN 15603 (electricity: 3.14, natural gas: 1.36)
The results show that the lowest primary energy savings are achieved by the local system A,
independent of the set of primary energy factors. But in case of the central system and the
local system B, the results are different and strongly dependent on the primary energy fac-
tors used.
Assuming the primary energy factors according to EnEV 2014, the central system is charac-
terized by the highest primary energy saving (figure 11). Assuming the primary energy fac-
tors of the EN 15603, the highest primary energy saving can be achieved by the local sys-
tem B (figure 12).
These results concerning the primary energy saving show, that a simple, local shower tray
heat recovery system without great technical effort such as e.g. a heat pump is, considering
the primary energy saving, competitive with central systems. Nevertheless, the main disad-
vantage of the investigated local shower tray heat recovery systems is the fact, that only a
part of the total grey water can be used for heat recovery. That’s why local systems taking
into account the whole grey water flow rate might offer even a higher heat recovery potential.
Finally, the results of this simulation study show a significant primary energy saving related to
the heat recovery from grey water. Further approaches aimed at the realization of additional
primary energy savings with regard to the energy supply of districts like the Jenfelder Au are
e.g. the realization of a high share of renewable energy sources for the energy supply and
the reduction of heat losses related to the heat distribution [Stübler et al. 2013].
page 16/208. Summary
In this article, typical values for the temperatures and flow rates of domestic grey water are
presented and discussed. Various types of grey water heat recovery systems are taken into
account and their advantages and disadvantages are compared. Three selected grey water
heat recovery systems, among them two local shower tray systems and one central system,
are investigated related to their thermal performance for the district Jenfelder Au in Hamburg
(Germany) with approximately 2,000 inhabitants.
The results of the study show that the heat recovery potential of the central grey water heat
recovery system is the largest, although high heat losses during the transport between the
buildings and the central point where the grey water heat recovery system is located occur.
Regarding the shower tray systems, the heat recovery potential is limited due to the fact that
the grey water flow rate can be used only partly for heat recovery.
In order to investigate the sensitivity of the three systems related to the primary energy sav-
ing, two current valid but highly different sets of primary energy factors based on EnEV 2014
(electricity 2.0, natural gas 1.1) and EN 15603 (electricity: 3.14, natural gas: 1.36) have been
used. In this context it is assumed that the heat recovered from the grey water, substitutes
the consumption of natural gas. The results show that the lowest primary energy saving is
obtained with the local system A, valid for both sets of primary energy factors. But in case of
the central system and the local system B, the results are different and strongly dependent
on the primary energy factors used. Assuming the primary energy factors of EnEV 2014, the
central system is characterized by the highest primary energy saving. Assuming the primary
energy factors of the EN 15603, the highest primary energy saving can be achieved by the
local system B.
Hence, concerning the primary energy saving, simple, local shower tray heat recovery sys-
tems without huge technical effort such as a heat pump are competitive with central systems.
However, the heat recovery potential of the investigated local systems is limited to the part of
grey water, accumulating in shower. Thus, it is worth to perform further research related to
local options allowing for the use of additional grey water flows e.g. from the washing ma-
chine and the dishwasher and also using a store to decouple the extraction of heat from the
grey water and the heat demand of the building.
In order to derive recommendations for the implementation of specific grey water heat recov-
ery systems beside the heat recovery potential and the achieved primary energy saving also
economic aspects have to be taken into account.
Acknowledgements
The project KREIS and the activities described in this article have been supported by the
German federal ministry of education and research (BMBF) under the grant agreement
n° FKZ 033 L047 A, FKZ 033 L047 D and FKZ 033 L047 B. The authors gratefully
acknowledge this support and carry the full responsibility for the content of this publication.
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