6 DHW heating with heat pumps

6.1 Hot water demand in buildings

There are different approaches in practice for determining needs. For residential buildings, the design is often based on DIN 4708-2 using the so-called NL-number (performance indicator of a normal apartment). However, this design and dimensioning method, which is valid for heating boilers, cannot generally be used for heat pump systems because NL Numbers of the storage tanks for the flow temperatures used in heat pump operation are hardly available. Therefore, it makes sense to carry out the design based on the amount of heat required. Several mutually influencing factors must be taken into account (see Section 6.1.1).

6.1.1 Determination of the hot water requirement for heating heat pumps

The design of the heating heat pump and the hot water storage tank should be based on the amount of heat required in the system. The following factors must be taken into account:

• the daily requirement

• the peak demand

• anticipated losses

• required hot water temperatures

• the available heating power for reheating the hot water storage tank

interpretation In order to be able to cover the hot water requirement of the building during the reference time, the required hot water output must be available either as stored hot water or as heating output.

1. For the design, the maximum daily hot water requirement and the corresponding consumption behavior must first be determined. In addition to real consumption values, average tapping profiles can also be used for this determination. These are shown in EN 15450 as an example for three user groups in Appendix E and can be expanded individually.

2. The period with the greatest power requirement is determined from the load profile. A memory size then results from this power requirement. When selecting the storage tank, it must be taken into account that there is heat loss due to heat dissipation from the surface (see heat retention losses S on the energy label of the storage tank) and mixing of the storage tank due to inflowing cold water.

Tab.6.1: Assumption of the dispensing volume according to EN 15450

** With rain showers, the average consumption is around 25 to 50% higher than with "classic" shower heads.

Tab.6.2: Average dispensing volume of an individual (36 liters; 60 ° C) according to EN 15450

Table 6.3: Average tap volume of a family (without bathing; 100 liters; 60 ° C) according to EN 15450

Tab.6.4: Average tap volume of a family (with bathing; 200 liters; 60 ° C) according to EN 15450

6.1.2 Design method for heating heat pumps in apartment buildings

The design is shown below using an example calculation for a multi-family house.

Building data

• Multi-family house with 6 residential units

• 3 people per unit

Determination of the reference period and the hot water requirement The reference period with the greatest energy requirement can be read from the corresponding design table in accordance with EN 15450. The following applies to the calculation example:

• Reference period from 8:30 p.m. to 9:30 p.m.

• Energy requirement for hot water preparation of 4.445 kWh per residential unit

Tab.6.5: Selection of the reference period

The energy requirement for the entire building during the reference period is determined from: Q_DPB = N_NE * Q_DPBNN
with:

• Q_DPB = Energy demand during a reference period in kWh

• Q_DPBNN = Energy demand of a usage unit during a reference period in kWh

• N_NE = Usage units with the same profile

1st step: Required energy requirements

• Q_DPBNN = 4.445 kWh

• N_NE = 6

• Q_DPB = 26.67 kWh

The required amount of hot water can now be determined from this:

with:

• V_DP = required amount of hot water during a reference period in liters

• Q_DPB = Energy demand during a reference period in kWh

• c_w = specific heat capacity 1.163 Wh / kgK of water

• t_target = Target storage tank temperature

• t_cw = Cold water temperature

Step 2: Required amount of hot water

• Q_DPB = 26.67 kWh

• c_w = 1.163 Wh / kgK

• t_target = 60 ° C

• t_cw = 10 ° C

• V_DP = 459 l

Selection of the hot water storage tank The storage volume including a surcharge for mixing losses results from:

with:

• V_Spmin = Minimum storage volume in liters

• V_DP = required amount of hot water during a reference period in liters

• DMV = mixing losses (15 to 20%)

3rd step: Volume of the hot water storage tank

• V_DP = 459 l

• DMV = 1.15 (corresponds to 15%)

• V_Spmin = 582 l

Variant 1 - storage tank with internal heat exchanger
Two hot water tanks with internal heat exchangers with a capacity of 390 l each are selected here. The storage losses are 2.78 kWh / 24h. The storage losses over the entire reference period are sufficiently taken into account in the larger storage volume. In the hot water storage tanks there is the option of using special accessories (e.g. DFM 1988-1 / DFM 1988-WPM) to guarantee the outlet temperature of ≥ 60 ° C in the upper third.

Fig.6.1: Series connection of hot water storage tanks

Variant 2 - load storage tank with external heat exchanger (e.g. fresh water station) A 750 l storage tank is selected here. The storage losses are 3.2 kWh / 24h. A storage tank outlet temperature of ≥ 60 ° C must also be guaranteed with this solution. Depending on the type of heat pump, the storage tank must be reheated using a second heat generator or directly electrically.

Fig. 6.2: Load storage tank with external heat exchanger

Selection of the heat pump

In the next step, the heating output of the heat pump required for warm water heating must be determined. This value is the required surcharge for warm water heating on the heating output of the heat pump and is based on the time available between the individual reference periods.

Tab. 6.6: Selection of the time between two reference periods

with:

• Q_WP = required heating output of the heat pump in kW

• V_Sp = Storage volume (total) in liters

• c_w = specific heat capacity 1.163 Wh / kgK of water

• t_target = Target storage tank temperature

• t_cw = Cold water temperature

• T_stop = Time between the reference periods in h

4th step: Selection of the heat pump

• V_Sp = 780 l (two storage tanks á 390 liters)

• c_w = 1.163 Wh / kgK

• t_target = 60 ° C

• t_cw = 10 ° C

• T_stop = 11.5 h

• QWP = 3.94 kW

The necessary heating output of the heat pump is heavily dependent on the time span between two reference periods. If the period of time is very short, the required heating power is significantly higher. In this case, alternatives can be considered. Either the storage tank size is increased by the value for the second reference period or a second heat generator for hot water preparation is provided as a bivalent heat generator. The latter can be the better solution from a cost perspective, since lower investment costs are incurred for tapping the primary source of the heat pump.
Review of the design If the heat pump is designed using the reference periods, a plausibility check should be carried out at the end of the calculation. The heating output determined for the heating-up time must be greater than the computationally necessary output with constant tapping over the entire day.

with:

• Q_WP = required heating output of the heat pump in kW

• Q_DPT = Power requirement for daily consumption in kW

• N_NE = Number of residential units with the same usage profile

5th step: Checking the calculation

• Q_DPT = 11.445 kWh / 24 h

• N_NE = 6

• Q_WP = 3.94 kW

• 3.94 kW> 6 * 11.445 kWh / 24 h

• 3.94 kW> 2.86 kW

6.1.3 Simplified procedure for heating heat pumps in single and two-family houses

In the one- and two-family house area with standard sanitary equipment, the required storage tank size and the required heating power can be determined with the help of a simplified procedure. A daily hot water requirement of 50 liters, based on a hot water temperature of 60 ° C, is assumed per person. To select a storage unit for up to 10 people, the minimum storage volume must first be determined. In addition, the daily hot water requirement is doubled. This minimum volume is converted to the actual storage temperature.

with:

• V_Sp = Storage volume (total) in liters

• V_tsoll = Hot water volume at t_target in liters

• V_DP60 = Hot water volume at 60 ° C in liters

• t_target = Target storage tank temperature

• t_cw = Cold water temperature

example

• V_DP60 = 200 l (4 people at 25 liters per person)

• t_target = 50 ° C

• t_cw = 10 ° C

• V_Sp = 250 l

6.1.4 General calculation bases for drinking water heating

Tab. 6.7: Calculation bases for drinking water heating

6.2 Hot water heating with the heating heat pump

In addition to regulating the heating, the heat pump manager also takes on the hot water preparation (see chapter Control). The integration of the hot water heating with the heat pump must take place in a separate hydraulic circuit, since different temperature levels are usually required for hot water and heating.

6.2.1 Requirements for the hot water storage tank

The standard continuous outputs specified by various storage tank manufacturers are not a suitable criterion for selecting the storage tank for heat pump operation. Decisive for the selection of the storage tank are the size of the heat exchanger surfaces, the construction, the arrangement of the heat exchangers in the storage tank, the standard continuous output, the flow rate and the arrangement of the thermostat or sensor.
The following criteria must be taken into account:

• Reheating as a result of standing losses without tapping (coverage of standing losses - static condition).

• The selected hot water storage tank must be able to draw the heating output made available by the heat pump even at the maximum heat source temperature (e.g. air +35 ° C).

• When a circulation line is operated, the storage tank temperature is reduced. The circulation pump should be controlled as required.

• The defined draw-off quantities must also be achieved during a blocking period, i.e. without reheating by the heat pump.

• Targeted reheating using a flange heater is only possible in conjunction with a temperature sensor inserted into the hot water storage tank.

6.2.2 Hot water storage tank for heating heat pumps

The hot water storage tanks are used to heat drinking water, e.g. for sanitary use. The heating takes place indirectly via a built-in smooth-tube heat exchanger through which the heating water flows or in accordance with the flow principle (fresh water systems).
Corrosion protection
Enamelled storage tanks are protected according to DIN 4753 Part 3 on the entire inner surface by a tested enamelling. In connection with the additionally built-in magnesium sacrificial anode, this guarantees reliable corrosion protection. According to DVGW, the magnesium sacrificial anode must first be checked by a specialist after 2 years and then at appropriate intervals and replaced if necessary. Depending on the drinking water quality (conductivity), it is advisable to check the sacrificial anode in shorter periods of time. If the anode (33 mm) is broken down to a diameter of 10-15 mm, it is recommended to replace it.

As an alternative to the magnesium anode, an impressed current anode (Correx anode) can also be used. This should be used if the magnesium sacrificial anode is broken down too quickly, the water smells unpleasant or too many air bubbles form when the water is drawn from the tap. The impressed current anode (titanium anode) must be connected directly to a voltage source (230 V ~) and is maintenance-free.
Water hardness Depending on the location / region, the drinking water contains more or less lime. Hard water means very hard water. There are different hardness ranges, which are measured as a unit in degrees of German hardness (° dH).

In Switzerland the term "French degrees of hardness" is used

When using electrical flange heaters for general reheating to temperatures above 50 ° C, we recommend water from hardness range III with a hardness> 14 ° d.H. (hard and very hard water) the installation of a decalcifying system.
Installation Before starting up the heat pump, check whether the water supply (cold water supply) is open and the storage tank is full. The first filling and commissioning must be carried out by an approved specialist company. The function and tightness of the entire system including the parts installed by the manufacturer (e.g. flange cover, flange heating) must be checked.
Cleaning and care The required cleaning intervals differ depending on the water quality and the level of the storage tank temperature. We recommend cleaning the storage tank and checking the system once a year. The enamelled smooth surface largely prevents limescale from sticking and enables quick cleaning, e.g. using a water jet. Large scale limescale may only be crushed with a wooden stick before rinsing. Sharp-edged, metallic objects must never be used for cleaning.

The function of the safety valve must be checked at regular intervals. Annual maintenance by a specialist company is recommended.
Thermal insulation and cladding
For storage tanks with a nominal capacity of up to 500 liters, the thermal insulation consists of high-quality PU (polyurethane) rigid foam which is foamed directly onto the storage tank wall. For storage tanks larger than 500 liters, the thermal insulation can be removed and consists of PE (polyethylene) or PS (polystyrene) foam with a foil jacket.
regulation The storage tanks are supplied as standard with a sensor (NTC 10 - DIN 44574) including a 5 m connection cable, which is connected directly to the heat pump manager as sensor R 3 and inserted into the immersion sleeve on the storage tank, ensuring good heat transfer. The temperature setting, time-controlled charging and, if necessary, reheating by means of flange heating is carried out by the heat pump manager. The hysteresis must be taken into account when setting the target hot water temperature. The hysteresis is subtracted from the setpoint specification and defines the switch-on point of the heat generator. For example, setpoint 50 ° C - hysteresis 7 K results in a switch-on temperature of 43 ° C and a switch-off temperature of 50 ° C.

Alternatively, control can be carried out with an external thermostat. The hysteresis should not exceed 2K (2-point controller).
Operating conditions:

Tab 6.8: Permissible operating conditions

Assembly
The assembly is limited to the hydraulic integration including safety devices and the electrical connection of the sensor.
equipment
Flange heaters with leakage resistance (insulated installation), designed for enamelled hot water storage tanks, for thermal disinfection are available as accessories. The screw-in heating elements of the CEHK series can also be installed in enamelled hot water storage tanks with an additional screw socket 1 ½ ". The screw-in heating elements CTHK have no leakage resistance and must therefore not be used for enamelled storage tanks.

Fig. 6.3: Structure of a flange heater

Tab.6.9: Legend of flange heating

Fig. 6.4: Structure of the screw-in heater CEHK
Installation site
The storage tank may only be set up in a frost-free room. Installation and commissioning must be carried out by an approved specialist company.
Water-side connection
The cold water connection must be carried out in accordance with DIN 1988 and DIN 4573 Part 1 (see Fig. 6.5).

Since a circulation line causes high standby losses, it should only be connected to a widely ramified drinking water network. If circulation is required, it must be equipped with an automatically acting device (e.g. time or pressure controlled) to interrupt the circulation operation.

All connection lines including fittings must be insulated against heat loss in accordance with country-specific standards (e.g. Germany Energy Saving Ordinance (EnEV)). Poorly or not at all insulated pipe connections lead to an energy loss that is many times greater than the energy loss of the storage tank itself. A check valve must be provided in the heating water connection to avoid uncontrolled heating or cooling of the storage tank. The discharge line of the safety valve (safety valve combination) in the cold water supply line must always remain open. The operational readiness of the safety valve must be checked regularly for function, e.g. by venting it.

Emptying
A possibility of emptying the storage tank must be provided on site in the cold water connection pipe.
Pressure reducing valve
If the maximum network pressure can exceed the permissible operating pressure of 10 bar, a pressure reducing valve in the connection line is essential. However, in order to reduce the development of noise (e.g. pressure surges in the drinking water network), the line pressure within buildings should be reduced to an operationally permissible level in accordance with DIN 4709. For this reason, depending on the type of building, a pressure reducing valve in the storage tank inlet can be useful.
Safety valve
The system must be equipped with a component-tested safety valve that cannot be shut off towards the storage tank. No constrictions, such as dirt traps, may be installed between the storage tank and the safety valve.

When the storage tank is heated up, water must flow out (drip) from the safety valve in order to absorb the expansion of the water or to prevent an excessive increase in pressure. The discharge line of the safety valve must open freely, without any constriction, above a drainage device. The safety valve must be installed in an easily accessible and observable location so that it can be opened during operation. There is a sign near or on the valve itself with the inscription: “During heating, water can escape from the exhaust line! Do not close! "

Only component-tested, spring-loaded diaphragm safety valves may be used. The blow-off line must be at least as large as the safety valve outlet cross-section. If, for compelling reasons, more than two bends or a length of more than 2 m are required, the entire blow-off line must be one nominal diameter larger. In addition, like a sewer pipe, it should have a slight gradient away from the safety valve. It usually ends over a small collecting funnel to see whether water is escaping or not. More than three arches and 4 m in length are not permitted. The drainage line behind the collecting funnel must have at least twice the cross-section of the valve inlet. The safety valve must be set so that the permissible operating pressure of 10 bar is not exceeded.
Check valve, test valve
To prevent the heated water from flowing back into the cold water line, a non-return valve (non-return valve) must be installed. The function can be checked by closing the first shut-off valve in the flow direction and opening the test valve. Except for the water present in the short piece of pipe, no water may escape.
Shut-off valves
Shut-off valves are to be installed on the storage tank shown in Fig. 6.10 in the cold and hot water connection as well as the heating water flow and return, making sure that the fittings are suitable for drinking water (e.g. KTW approval).

Legend Shut-off valve Pressure reducing valve Test valve Backflow preventer Pressure gauge connection piece Drain valve Safety valve Circulation pump Drain Hot water Circulation (if necessary) Heating water flow * Heating water return * Cold water connection according to DIN 1988

Fig.6.5: Water-side connection

Pressure drops
When dimensioning the charge pump for the hot water storage tank, the pressure losses of the internal heat exchanger must be taken into account.
Temperature setting for hot water preparation with the heating heat pump
Low temperature heat pumps have a maximum flow temperature of up to 60 ° C. This temperature must not be exceeded during hot water preparation so that the heat pump does not switch off via the high pressure pressure switch. Therefore, the temperature set on the controller should be below the maximum attainable storage tank temperature.

The maximum achievable storage tank temperature depends on the output of the installed heat pump and the heating water flow rate through the heat exchanger (smooth tube heat exchanger). The maximum achievable hot water temperature for heating heat pumps can be determined according to chap. 6.2.3 take place. It should be taken into account that the amount of heat stored in the heat exchanger leads to a further reheating of approx. 3K. In the case of hot water preparation with the heat pump, the set temperature can be 2 to 3 K below the desired hot water temperature.

6.2.3 Achievable hot water storage tank temperatures

The maximum hot water temperature that can be achieved with the heat pump depends on:

• the heating output (heat output) of the heat pump

• the heat exchanger surface installed in the storage tank and

• the delivery rate (volume flow) of the circulation pump.

The selection of the hot water storage tank must be based on the maximum heating output of the heat pump (summer operation with air / water heat pumps or high heat source temperatures with brine / water heat pumps) and the desired storage tank temperature (e.g. 50 ° C).

When designing the hot water charging pump, the pressure losses in the storage tank must be taken into account.
The maximum achievable hot water temperature depends on the factors listed above.
If the set hot water target temperature (see also chapter Control and regulation) is selected too high, it cannot be achieved in pure heat pump operation. The set target hot water temperature can still be achieved by means of flange heating and activated reheating.
If a hot water temperature of 40 ° C is reached in the storage tank in pure heat pump operation, it is advisable to check the above factors.

If the power provided by the heat pump cannot be transferred to the hot water storage tank, the pressure in the cooling circuit increases. When the maximum permissible pressure is reached in the cooling circuit, the high-pressure safety program automatically switches off the heat pump and blocks hot water heating for a maximum of 2 hours.

In hot water storage tanks with sensors, the integrated learning function automatically adjusts the maximum achievable temperature - before the maximum pressure is reached. Means: DHW temperature maximum new = current actual temperature in the DHW cylinder - 1 Kelvin.

If higher hot water temperatures are required, this can be done via

• electrical reheating (flange heating in the hot water storage tank)

• 2. Heat generator (oil or gas boiler, pellet boiler, etc.)

take place.

Example:
Heat pump with a maximum heating output of 14 kW and a maximum flow temperature of 55 ° C
Hot water tank 400l storage
Volume flow of the hot water charging pump: 2.0 m³/H The result is a hot water temperature of: ~ 47 ° C

Fig.6.6: Design of a hot water storage tank using the example of WWSP 442

Calculation of the heat exchanger capacity (register capacity)

The performance of the registry depends on several factors:

• Area of the register

• Material property

• Operating conditions

The performance of the register can be calculated from this:

Q = ∝ * A * ∆Tm

Example:

4 m² Register surface in an enamelled steel container, heating side flow / return = 58/48 ° C, cold water inlet of 10 ° C, hot water temperature 45 ° C.

This results in the following mean temperatures: 53 ° C on the heating side and 27 ° C on the domestic water side and a mean temperature difference ΔT_m from 26 K

Calculation of the draw-off quantities (continuous output)

Example:
With a register output of 32.2 kW, water should be heated from 10 ° C to 45 ° C.

So 219 g or 200 ml of water are heated from 10 ° C to 45 ° C per second. That corresponds to 13 liters per minute or 788 liters per hour.

6.2.4 Design aid for combination and hot water storage tanks

The table shows the allocation of hot water charging pumps and storage tanks to the individual heat pumps in which a hot water temperature of 45 ° C is reached in 1-compressor heat pump operation (maximum temperatures of the heat sources: air: 25 ° C, brine: 10 ° C, water 10 ° C, maximum Pipe length between heat pump and storage tank 10 m). The maximum hot water temperature that can be reached in pure heat pump operation depends on:

• the heating output (heat output) of the heat pump

• the heat exchanger surface installed in the storage tank

• the volume flow as a function of the pressure loss and delivery rate of the circulation pump.

Tab.6.10: Design aid for combination and hot water storage tanks

6.2.4.1 Legionella

6.2.4.1.1 How do legionella bacteria develop in drinking (warm) water installations

Legionella are mostly found in stagnant water and occur at a water temperature between 25 ° C and 55 ° C. Possible causes promote the occurrence of legionella:

• Stagnation due to oversizing of the drinking water pipes

• Excessive saving of water by users

• Vacancy (e.g. unleted residential unit) or longer absence of residents (e.g. holiday home)

• Lime and sludge deposits in pipelines and hot water storage tanks, especially in "older" buildings

• Missing hydraulic balancing of the drinking water pipe

• Insufficient insulation of the cold and hot water pipes

• Incorrect energy saving by reducing the flow temperature of the heat generator

6.2.4.1.2 How can Legionella be avoided or removed in the drinking (warm) water installation

Thermal disinfection
Thermal disinfection is the best method of preventing legionella in drinking water today. From a temperature of 55 ° C legionella can no longer multiply, from a water temperature of 60 ° C they die. In order to ensure that Legionella is killed, the tapping points must be rinsed with hot water (> 60 ° C) for at least 3 minutes; in the case of large objects and drinking water systems, this must be done by strands.
Disadvantages: The high temperatures during "rinsing" make the material more susceptible to corrosion, in particular welding seams, soldered joints or seals are heavily stressed, and the high temperatures also cause more limescale to precipitate and deposit in the pipelines.

Legionella circuit
The legionella switch is a periodic, thermal disinfection that is intended to counteract the growth of legionella. The hot water storage tank or drinking water heater and the entire hot water network including the tapping points are heated to temperatures> 70 ° C for at least 3 minutes in a defined cycle. It is important that all draw-off or tap points are open. The legionella switch is a preventive measure and has no effect on already contaminated systems.

Legionella detection - test procedure
The drinking water from the water supply company is usually flawless and has a pH value between 6.5 and 9.5 when it leaves the waterworks. This range of the pH value is anchored in law. From the house feed to the extraction point, however, the drinking water can be polluted by various impurities in the pipe system, pipes and fittings by bacteria or heavy metals. A drinking water analysis with a rapid bacterial test can reliably and clearly identify and quantify possible contamination of the drinking water. This test is particularly recommended for spot checks after renovation work on the property, if there is any suspicion of contamination or health protection concerns.

Chemical disinfection
If the limit values of the Drinking Water Ordinance for microbiological parameters are exceeded in a drinking water installation, the microbial contamination must be removed immediately. The structural differences usually require an individual action plan that includes regular preventive measures such as flushing the pipe network or installing an ultrafiltration system. The disinfection of an already contaminated system is usually carried out sustainably and effectively by flushing the drinking water system with chlorine dioxide. This not only kills legionella, but also removes the biofilm that has settled in the pipelines. In contrast to pure chlorine, chlorine dioxide systems do not degrade the disinfection effect as the pH value rises, and it is very effective and odorless even at very low concentrations. This process should be carried out by a licensed specialist, as improper use can result in undesirable by-products.

6.2.4.2 Country-specific requirements for drinking water quality

6.2.4.2.1 Germany - DVGW - Worksheet W 551

The DVGW worksheet W 551 defines construction and operating requirements for systems for the provision of hygienically perfect drinking hot water with special consideration and measures to reduce the growth of legionella in drinking water systems. Be differentiated Small systems (One- and two-family houses) and Large systems (all other systems with storage capacity greater than 400 liters and a pipe capacity greater than 3 liters between storage facility and tapping points).

Requirements for small systems

1. Delimitation / general:

   1. Volume of the Drinking water storage tank <400 liters (does not apply to one- and two-family houses)

   2. Line volume¹⁾ <3 liters

   3. It is necessary to inform the user about health risks when operating at low temperatures

2. Construction requirement:

   1. It must be possible to reach an outlet temperature of> 60 ° C at the drinking water storage tank

3. Operational requirement:

   1. no specifications for operating temperature, but:

      • Recommendation> 60 ° C at the outlet of the drinking water storage tank

      • Temperatures <50 ° C should be avoided

   2. If necessary (after a long standstill): thermal disinfection²⁾ recommended

4. Summary:
   For small systems, it is recommended to set the temperature on the drinking water storage tank to 60 ° C. However, operating temperatures below 50 ° C should be avoided in any case. When using low-temperature heat pumps, for reasons of economy, post-heating in the hot water storage tank should be carried out using an additional electrical heater.

Requirements for large systems

1. Demarcation

   1. Volume of the drinking water storage tank> 400 liters (does not apply to one- and two-family houses) or

   2. Line volume¹⁾ > 3 liters

2. Construction requirements:

   1. Complete heating of the drinking water storage tank must be possible (mixing equipment may be required for this)

   2. With line volume¹⁾ > 3 liters a circulation line is required

3. Operational requirement:

   1. Outlet temperature at the drinking water storage tank> 60 ° C; Short-term, operationally-related shortfalls are permissible (e.g. removal)

   2. Operating temperature of the entire system permanently> 55 ° C. Therefore: drop in temperature stratification up to the connection point of the circulation line in the drinking water storage tank <5 K)

   3. 1x complete heating of the drinking water storage tank> 60 ° C per day

4. Summary:
   In large systems, either the water at the hot water outlet of the storage tank must be heated to at least 60 ° C. Alternatively, the entire storage volume (usable content) can be exchanged within 72 hours.
   

¹⁾ "Line volume" refers to the content of a pipeline from the drinking water heater to the tapping point without the content of the return to the drinking water heater via a circulation line. The individual pipelines are considered, not the total volume of the pipeline system.
²⁾ A minimum of 70 ° C is required for thermal disinfection. This temperature does not necessarily have to be made available by the drinking water heater. External additional heating is also possible.

Tab. 6.11: Water content per pipe length for different pipe cross-sections

6.2.4.2.2 Switzerland - SVGW leaflet TPW

The leaflet "Legionella in drinking water installations - what must be considered?" Shows where problems with legionella can occur in drinking water and what options exist to effectively reduce the risk of legionella disease.

6.2.4.3 Accessories for hot water preparation - flow rate measurement DFM 1988-1 / DFM 1988-WPM

The flow meter DFM 1988 is a measuring and control device with which the tap volume of a central drinking water storage tank at the cold water inlet is recorded. According to DIN 1988-200, the storage tank temperature may be reduced to a minimum of 55 ° C with high hot water exchange. This enables the hot water tank to be heated more efficiently (e.g. with a heat pump).
functionality
If the requirement for drinking water installations after a complete exchange of the drinking water in the storage tank is not met within 72 hours, a switching output on the electronics unit of the DFM 1988 is released to control a second heat generator (electric immersion heater). This enables the drinking water in the storage tank to be heated to a temperature of more than 60 ° C. The required setpoint is maintained until the required water exchange has taken place within 72 hours. The switching output for the second heat generator is active until the switch-off temperature of 62 ° C has been reached. It is switched on again at 60 ° C.

The system installer must dimension the system so that the required water exchange is usually achieved within 3 days. The DFM 1988 is used as a safeguard to automatically increase the hot water temperature to 60 ° C if the water exchange is too low. The heat pump system - consisting of heat pump and storage tank - is to be designed in such a way that 55 ° C is reached in pure heat pump operation under normal conditions. In normal operation with high water exchange, the DFM 1988 does not generate any additional energy expenditure for the electric immersion heater in the hot water storage tank, as the heat pump generates a hot water temperature of 55 ° C. In systems without DFM 1988-1 in which the increased water exchange cannot be ensured, the system must be operated continuously at 60 ° C. In systems with permanently programmed locking times for the energy supplier (e.g. 3 x daily up to 2 hours), the system should be programmed so that the hot water temperature is increased to 60 ° C before this locking time.

Establishment of the DFM in 1988

The DFM 1988 consists of an electronic module for wall mounting, a turbine sensor for determining the amount drawn off and an NTC-10 temperature sensor.

Fig.6.7: Hydraulic structure of the DFM 1988-1

According to DIN 1988-200, hot water temperatures of greater than 50 ° C are permissible if the hot water installation can be exchanged within 3 days during operation. If you take into account the use of a circulation line with a heat loss of 5 Kelvin in the return line, the hot water outlet temperature must be at least 55 ° C.

As a result, the heat pump used must be able to permanently provide a hot water temperature of 55 ° C in the storage tank during normal operation, depending on the heat output of the heat pump, the hot water tank used and the volume flow.

The following heat pumps achieve a maximum hot water outlet temperature of 55 ° C under the following conditions in pure heat pump operation

_{* Alternatively, changeover heating / hot water generation with 3-way changeover valve DWV 32, DWV 40, DWV 50.}

_{The hot water temperature displayed by the heat pump manager may differ from the hot water outlet temperature depending on the positioning of the sensor}

Tab.6.11a: Permissible system configurations heat pump, DFM 1988-1 and hot water storage tank

6.2.5 Hydraulic interconnection of hot water storage tanks

6.2.5.1 Interconnection of the combination memory PWD 750

The following drawing shows the hot water preparation via a combination storage tank PWD 750 with circulation line. In normal tapping operation, part of the drinking water is fed through the heat exchangers of the PWD 750 and heated. The desired hot water target temperature is regulated via the built-in 3-way valve. When the circulation pump is activated, part of the water is fed through the bypass into the upper right-hand heat exchanger and heated there. The thermostatic 3-way valve then mixes the heated water in the circulation line until the desired temperature is reached.

Cold water inlet PWD 750

Fig. 6.8: Integration of the circulation return in the cold water inlet of the thermostatic mixer

6.2.5.2 Combination of several hot water tanks

In the event of a high water requirement and the resulting heat pump output, the heat exchanger surface required for this can be implemented by connecting the heat exchanger surfaces of hot water storage tanks in parallel or in series. This is usually necessary with heat pump outputs of approx. 28 KW for hot water preparation in order to achieve sufficiently high hot water temperatures.

Fig. 6.9: Parallel connection of hot water storage tanks

the Parallel connection is only possible with identically constructed hot water storage tanks. When interconnecting the heat exchanger and the hot water connection, the pipes from the T-piece to both storage tanks must have the same pipe diameter and length (Tichelmann principle) in order to evenly distribute the volume flows for loading and unloading with an identical pressure loss. (see Fig.6.9)

Fig. 6.10: Series connection of hot water storage tanks

In the Series connection In the case of hot water storage tanks, it must be taken into account that the heating water is first fed through the storage tank from which the warm drinking water is taken. In addition, the higher pressure losses in contrast to the parallel connection must be taken into account when designing the hot water charging pump (see Fig. 6.10).

6.2.6 Storage tank for DHW preparation WWSP

6.2.6.1 Overview table DHW storage tank WWSP

¹Room temperature 20 ° C; Storage temperature 65 ° C

Tab.6.12: Technical data of the DHW cylinder WWSP

6.2.6.2 DHW cylinder WWSP 229

6.2.6.3 DHW cylinder WWSP 335

6.2.6.4 DHW cylinder WWSP 442

6.2.6.5 DHW cylinder WWSP 556

6.2.6.6 DHW cylinder WWSP 770

6.3 Hot water preparation with fresh water stations

6.3.1 Key figures for the design of fresh water stations

In order to design a fresh water station, it is necessary to know the respective tap volume of the building. The typical hot water consumption for various consumers can be read from the following table.

Tab.6.13: Typical hot water consumption

6.3.2 How a fresh water station works

The fresh water station supplies the tapping points with fresh hot water. The warm water is only heated when required using the flow principle via a stainless steel plate heat exchanger.

Stainless steel plate heat exchanger Digital fresh hot water controller Circulation pump 3a) Circulation pump circulation (optional) Volume flow meter check valve 5a) Check valve circulation 8) ball valve 9) temperature sensor 10) Angle seat valve 11) Ball valve (DVGW) A) Flow buffer storage B) Buffer tank return C) hot water D) cold water E) Connection to circulation F) circulation

Fig. 6.16: Functional representation of the fresh water station

The energy is supplied by heating water with a flow temperature of at least 50 ° C from a buffer storage tank. The buffer temperature determines the maximum hot water temperature. The heating water is fed to the heat exchanger in the fresh water station by a circulating pump that is regulated as required.

In adequately dimensioned fresh water stations, the heating water is usually cooled to temperatures of 20 ° C to 30 ° C. Mixing in the buffer storage tank is to be avoided so that the highest possible pouring capacity can be achieved. This applies in particular to the loading with the heat pump due to its maximum spread of approx. 10 K. To prevent mixing of the buffer in the upper area, the flow of the heat pump can be integrated in the middle area, depending on the buffer storage used. If this is not possible, a mixing valve must be installed to increase the heat pump return (return increase). By increasing the return, sufficiently high flow temperatures can be achieved. A return increase during tapping ensures that it can be used with heat pumps.

6.3.3 Hydraulic integration of fresh water stations

Fig. 6.17: Hydraulic integration of the fresh water station with return flow increase

Fig. 6.18: Functional diagram of the fresh water station with circulation connection

6.3.4 Integration schemes for hot water preparation

6.3.5 Legend

Tab.6.14: List of abbreviations for integration schemes

	thermostatically controlled valve
	Three-way mixer
	Four-way mixer
	Expansion tank
	Safety valve combination
	Temperature sensor
	leader
	Rewind
	Heat consumer
	Shut-off valve
	Stop valve with check valve
	Stop valve with drainage
	Circulation pump
	Overflow valve
	Three-way switch valve with actuator
	Two-way valve with actuator
	Safety temperature monitor
	High-performance deaerator with microbubble separation
	Electric immersion heater (pipe heating)
	Mud flaps
	Expansion tank
	thermostat

Tab.6.15: List of symbols for integration schemes

6.3.6 Integration of hot water preparation

DHW heating with switching valve YM 18  A heating circuit with a double differential pressure-free distributor	configuration	setting
Fig.6.19: Integration scheme for monoenergetic heat pump operation with one heating circuit, Row buffer storage and hot water preparation	Mode of operation electric heating	Additional heating in the buffer
	Heating circuit	Heat
	Heating circuit	no
	Hot water	yes with feeler
	Flange heating	Yes
	swimming pool	no
	Ensuring the heating water throughput via a double differential pressure-free distributor. The use of the double differential pressure-free distributor DDV is recommended for connecting all heat pumps. The circulation pump (M16) in the generator circuit is only in operation when the compressor is running in order to avoid unnecessary running times. The hot water generation is carried out with the additional circulation pump (M16) and closing changeover valve (YM18).

DHW heating with circulation pump M 18  A heating circuit with a double differential pressure-free distributor	configuration	setting
Fig.6.20: Integration scheme for monoenergetic heat pump operation with one heating circuit, Row buffer storage and hot water preparation	Mode of operation electric heating	Additional heating in the buffer
	Heating circuit	Heat
	Heating circuit	no
	Hot water	yes with feeler
	Flange heating	Yes
	swimming pool	no
	Ensuring the heating water throughput via a double differential pressure-free distributor. The use of the double differential pressure-free distributor DDV is recommended for connecting all heat pumps. The circulation pump (M16) in the generator circuit is only in operation when the compressor is running in order to avoid unnecessary running times. The hot water generation is carried out with the additional circulation pump (M16) and closing changeover valve (YM18).

6.4 Hot water heating with the hot water heat pump

The hot water heat pump is a ready-to-connect heater and essentially consists of the hot water storage tank, the components of the refrigerant, air and water circuit, as well as all the control, regulating and monitoring devices required for automatic operation. The hot water heat pump uses the heat of the sucked in air for hot water preparation with the supply of electrical energy.

As the temperature of the air drawn in falls, the heat pump heating output decreases and the heating-up time increases. The profitability of the operation increases with increasing air intake temperatures.
The water-side installation must be carried out in accordance with DIN 1988. The hot water heat pump is wired ready for connection, just plug the power plug into the earthed socket installed on site.

An additional electric immersion heater is integrated in the hot water heat pump. This fulfills several functions:

Additional heating
By operating the heat pump in parallel, the heating time for the water is shortened.

Frost protection
If the air inlet temperature falls below 8 ± 1.5 ° C, the electric heating element switches on automatically and heats the water (nominal) up to the set hot water temperature. With the DHW heat pump, the heating element is automatically switched on below -8 ° C + -1.5 ° C and the heat pump mode is deactivated. Below a temperature of 8 ° C, the heating element is switched on if the set target temperature has not been reached after a period of 8 hours. This function is inactive if the domestic water is heated by a second heat generator via the internal heat exchanger. The hot water temperature generated by the heating element in the frost protection function can rise above the set value!

Emergency heating
If the heat pump malfunctions, the hot water supply can be maintained by the heating rod.

Thermal disinfection
Water temperatures above 60 ° C (up to 75 ° C) can be programmed on the control panel keypad in the thermal disinfection menu. These temperatures are above 60 ° C by the electr. Reached the heating element. To achieve higher temperatures, the adjusting screw on the housing of the temperature controller must be turned to the right stop.

Condensate drain The condensate hose is attached to the rear of the device. It is to be laid in such a way that the accumulating condensate can flow off without hindrance and is to be drained into a siphon.

6.4.1 Functional description of the hot water heat pump

Various operating modes or time programs can be set on the controller of the hot water heat pump. With some types it is still possible to connect a second heat generator via an integrated heat exchanger. All hot water heat pumps can be combined with a photovoltaic system thanks to the SG Ready function.
Modes of operation
A maximum of two independent blocking times can be programmed on the controller. During the blocking times, the storage tank is kept at an adjustable minimum temperature in order to avoid a loss of comfort. All other programs are possible during this time. The storage tank is re-heated by the integrated heating rod as soon as the heat pump's area of application is not reached. In addition, the 'Rapid heating' button can be used to select whether the heating element should be active within a certain time or whether it should be permanently active.

ventilation
The ventilation function can be activated manually. It comes into play when the heat pump is off, i.e. there is no hot water requirement. The fan of the heat pump continues to run according to the set target value. This should ensure a minimum amount of exhaust air regardless of the heat pump operation, e.g. in the case of commercial waste heat utilization.

Combination with a second heat generator
With the help of the integrated pipe heat exchanger, an existing heat generator (2nd heat generator) or a solar system can be used to heat the storage tank. For this purpose, a circulation pump can be controlled by the integrated control.

The use of a second heat generator must be activated in the menu. It is requested when the heat pump's areas of application are left. This means if the lower or upper air inlet limit or the maximum permissible hot water temperature are exceeded. In this case, the 2nd heat generator has priority over the electric immersion heater in the heat pump. When activating the 2nd heat generator, a changeover temperature can also be selected that deviates from the lower application limit of the air temperature. If this temperature is not reached, the heat pump operation is blocked from the set temperature and the 2nd heat generator is used.
Alternatively, the hot water heat pump can also be operated in combination with a solar thermal system. As soon as a solar yield is recognized, the solar circulation pump is switched on and the heat pump is blocked. If there is no more solar yield or if a temperature limit value on the collector or in the storage tank is exceeded, the circulation pump is switched off again. The solar function has priority over the heat pump operation and the immersion heater.

Combination of hot water heat pump and a photovoltaic system
Hot water heat pumps can also be combined with a photovoltaic system. For this purpose, the controller of the heat pump can be connected to an additional evaluation unit (e.g. inverter) via a potential-free input - this must have a potential-free normally open contact. If sufficient power is available from the photovoltaic system in the "Photovoltaic" mode, the heat pump starts via the normally open contact and regulates to an adjustable, higher hot water setpoint for photovoltaic operation. The solar function has priority over the photovoltaic function. The operation of the heat pump with electricity from the photovoltaic system is shown on the display.

Fig. 6.21: Hot water heat pump combined with a photovoltaic system

If the output of the photovoltaic system is insufficient, the hot water heat pump is operated exclusively with electricity from the energy supplier's network. Excess solar power is fed into the power grid via an inverter.

In the case of hot water heat pumps with an internal additional heat exchanger, a relay with a potential-free contact automatically switches on a second heat generator if required.

Fig. 6.22: Connections and dimensions of the hot water heat pump with internal Additional heat exchanger ¹⁾ alternative condensate flow

Fig. 6.23: Connections and dimensions of the hot water heat pump BWP 30HLW with internal additional heat exchanger

6.4.2 Installation

The following applies to the choice of the device location:

• The hot water heat pump must be installed in a frost-free and dry room.

• Furthermore, the installation and the air intake must not take place in rooms that are potentially explosive due to gases, vapors or dust.

• The air drawn in must not be excessively contaminated or heavily dusted.

• If the installation room cools down due to the operation of the hot water heat pump, the room must be insulated from adjacent living spaces to avoid moisture damage (thermal bridges).

• The resulting condensate must be drained away frost-free.

• The subsurface must have sufficient load-bearing capacity.

• For trouble-free operation as well as for maintenance and repair work, minimum clearances must be observed in accordance with the installation and operating instructions.

Fig. 6.24: Installation conditions for free sucking in and blowing out of the process air. ^*) The minimum distance between the outlet opening of the air duct and the wall is 1.2 m

Optionally, air lines can be connected on both the intake and the exhaust side, which must not exceed a total length of 10 m. Flexible, sound and heat insulated air hoses DN 160 are available as accessories.

6.4.3 Air flow variants

Variable switching of the intake air
A pipe duct system with integrated bypass flaps enables variable use of the heat in the outside or room air for hot water preparation (lower limit of use: + 8 ° C).

Fig. 6.25: Variable switching of the intake air

Cooling in recirculation mode Room air is extracted via an air duct, e.g. from the storage room or wine cellar, cooled in the hot water heat pump, dehumidified and blown back in. The hobby, heating or utility room is suitable as a set-up location. To avoid the formation of condensation water, air ducts in the warm area must be insulated in a diffusion-proof manner.

Fig.6.26: Cooling in recirculation mode

Dehumidification in recirculation mode Dehumidified room air in the utility room supports laundry drying and prevents moisture damage

Fig. 6.27: Dehumidifying in recirculation mode

Waste heat is useful heat
The optionally built-in heat exchanger of a hot water heat pump enables direct connection to a second heat generator, e.g. solar system or boiler.

Fig. 6.28: Use of waste heat with a domestic water heat pump

6.5 Residential ventilation units with hot water generation

New materials and building materials are the cornerstones for a significantly reduced use of heating energy. Optimized insulation with a tight outer shell of the building ensures that almost no heat is lost to the outside. Extremely airtight windows in particular prevent the necessary exchange of air in old and new buildings. An effect that heavily pollutes the air in the room. Water vapor and pollutants accumulate in the air and must be actively ventilated.
Correct ventilation, but how?
Probably the simplest type of living space ventilation is the air renewal via an open window. Regular boost ventilation is recommended to maintain an acceptable indoor climate. This activity, which has to be carried out several times a day in all rooms, is annoying, time-consuming and often not feasible due to living and working habits alone.

Automatic living space ventilation with heat recovery ensures that the air exchange that is necessary from a hygienic and structural point of view is energy and cost-conscious.
Advantages of home ventilation devices

• Fresh, clean air without indoor air pollutants and excessive humidity

• Automatic assurance of the necessary number of air changes without any active intervention

• Reduced ventilation losses through heat recovery

• Integrable filters against insects, dust and dust-like air pollutants

• Shielding from outside noise and increased security with closed windows

• Positive evaluation according to the Energy Saving Ordinance (EnEV)

The use of mechanical home ventilation with heat recovery is indispensable in many cases. Before deciding on a ventilation system, the way in which waste heat is used should be clarified.
For the ventilation of residential units, it makes sense to use the exhaust air as an energy source for hot water, as it is in a building all year round there is a need for both ventilation and hot water. If there is an increased demand for hot water, a second heat generator must also be integrated.

6.6 Convenience and cost comparison with different options for warm water heating

6.6.1 Decentralized hot water supply (e.g. electrical instantaneous water heater)

advantages

• low investment

• extremely low space requirement

• no additional heating power requirement for the hot water preparation of the heating heat pump necessary

  • no downtime and circulation losses

disadvantage

• higher operating costs

• higher network connection capacities and cable cross-sections required

6.6.2 Electric storage tank

advantages

• low investment

• higher hot water temperatures in the storage tank possible

• greater availability of the heat pump for heating (especially with monovalent operation and blocking times).

  • Use of photovoltaics possible (self-consumption)

disadvantage

• higher operating costs

  • more calcification at higher temperatures

  • longer heating times

6.6.3 Hot water heat pump

advantages

• A cooling or dehumidifying effect can be achieved at the installation site (e.g. storage cellar) in summer

  • no additional heating power requirement for the hot water preparation of the heating heat pump necessary

• easy integration of solar thermal and photovoltaic systems

• higher hot water temperatures in pure heat pump operation

disadvantage

• long reheating times of the hot water storage tank due to low post-heating output

  • Cooling down of the installation room in winter (with room air dependent operating mode)

6.6.4 Apartment ventilation unit with hot water generation

advantages

• comfortable home ventilation to ensure hygienic air exchange

• Hot water preparation through year-round active heat recovery from the exhaust air

• greater availability of the heat pump for heating (especially with monovalent operation and blocking times)

  • easy integration of solar thermal systems

• higher hot water temperatures in pure heat pump operation

disadvantage

• Significantly longer reheating times for the hot water storage tank in heat pump operation

• If there is a high demand for hot water, it must be combined with a second heat generator

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