4 Planning instructions and standard circuits for heat-
ing, cold water and chilled water supply
4.1 General
4.1.1 Design pressure
When a central energy supply is used, all system components should be designed for
pressure stage PN 10.
If an existing building must be connected to a central supply but its system is not de-
signed for pressure stage PN 10 or requires a higher pressure stage than PN 10, the
building should be connected indirectly via a heat exchanger.
For heating systems, preferably tubed heat exchangers or brazed plate heat exchang-
ers should be used. Bolted plate heat exchangers should be avoided wherever possi-
ble in heating systems, since they are liable to leak when subjected to large fluctua-
tions in temperature.
For cold and chilled water systems, preferably bolted plate heat exchangers should be used to exploit the small temperature difference necessary between primary and sec-
ondary feeds.
4.1.2 Fittings
4.1.2.1 Shut-off fittings
To minimize pressure loss, preferably shut-off butterfly valves should be used. For
sizes < DN 40, compact or supercompact valves should be used. In special cases,
ball valves or gate valves may be used.
In the inflow to systems that should be fed with an exact water quantity, shut-off val-
ves with integral mass flow sensors (e.g: KSB BOA-Control IMS) should be fitted.
Where no calibrated heat quantity meters are required, the measurement signal
from the building automation may also be used to measure heat consumption.
For quicker filling and draining, larger distributors should be fitted with a DN 50 shut-
off valve and a C-coupling.
At each inlet and outlet of cooling machines, heat exchangers and other system
components that have to be cleaned regularly with a liquid cleaning agent, a shut-off valve and a C-coupling should also be installed, so that the liquid cleaning agent
can be pumped through the component without the component having to be discon-
nected from the pipe network.
4.1.2.2 Strainers
Strainers should be used "sparingly", since their disadvantages (clogging, mainte-
nance effort) often exceed their benefits.
Strainers must be installed before fittings with safety functions such as:
?oil and gas burners, and furnaces
?Safety shut-offs for combustible and hazardous liquids and gases
?Systems that may cause damages if valves fail to close (e.g. flooding, overheat-ing, undercooling)
?Control and safety valves in the inflow to heat exchangers
?Control valves in the inflow to manufacturing equipment
?Equipment for which strainers are fitted for component testing for legal ap-proval.
?Equipment for which strainers are officially specified by a regulatory authority.
?Components where the manufacturer demands a strainer is fitted in the inflow.
In all other cases, strainers can usually be dispensed with.
Where a strainer is fitted, pressure gauges should be fitted before and after it, to
monitor the degree of clogging.
For strainers > DN 100, the cover should be provided with a drain cock.
4.1.2.3 Return temperature limiters
At the end of long supply pipes, a bypass pipe with a return temperature limiter
should be fitted, so that at little or no load, a certain minimum quantity of water flows through the pipe, thus improving the response behavior of the consumers.
Figure 4-1: Bypass pipe with return temperature limiter (for example, heating systems)
Return temperature limiters should also be fitted to ceiling air heaters, wall air heaters, door air curtains and small recirculating air cooling devices to improve their response
behavior and at the same time stay within the planned return temperature level.
4.1.3 Pipework design
Pipework for heating and cooling systems is usually sized so that the pressure loss
is < 100 Pa/m.
Pipework that is exposed to humidity, or on which condensation can form (e.g: cold
water pipes), should be painted with anti-corrosion paint.
Pipework should be mounted to provide noise protection. See Chapter 12 for details
4.1.4 Pumps
Larger supply networks should be supplied by several pumps in parallel. One pump
shall have variable speed drive by means of a frequency converter, so that at the
most distant building distributor, a pressure differential of approx. 0.3 bar is still
achieved. The minimum circulation flow rate of the pump is ensured by a pressure
differential regulator at the building supply station (see diagram below).
The frequency converter is designed for one pump motor, however, it can be
switched to any pump motor. The three-phase motors of glanded pumps (dry run-
ning) must satisfy energy efficiency class 1, be suitable for operation with frequency inverters to DIN IEC/TS 60034-17 and from 1.5 kW must be equipped with complete motor protection by thermistor temperature sensors.
Either the pump motor should be designed so that it is not overloaded even at low
pressure differentials and large water flow rates, or the pump must be fitted with a
throttle valve so that the pressure differential does not fall below a set value.
Figure 4-2: Network pump group diagram
Limitation of the max. volumetric flow rate Limitation of the max. volumetric flow rate by throttle valves by building automation (max. motor
power)
Figure 4-3: Pressure differential controller and dp-sensor for the network pump
Consumers for which a second supply source exists (e.g. static heating control group and ventilation control group) are fitted with individual pumps.
If an area or consumer is supplied by only a single control group and the failure of the pump would lead to an unacceptable consequence, that control group should be fitted with a double pump arrangement.
Consumer circuits with fluctuating water quantities should be fitted with variable-speed pumps. At the worst point of the consumer circuit, a pressure differential regulator should be provided so that at reduced flow rates and increased pressure differential, the pressure differential regulator opens and the necessary minimum flow rate for the pump is ensured, thus preventing the pump from overheating.
Figure 4-4: Example of pressure differential controller in the consumer circuit at the worst point of the system in the building
supply
4.2 Heat
4.2.1 Design temperatures for heat supply systems:
Inlet temperature Outlet temperature Heat generator
Boiler, boiler circuit 70 °C 90 °C
Boiler, condensing heat exchanger 45 °C 50 °C
Heat pumps 45 °C 50 (55) °C
Heat recovery compressed air 50 °C 60 (70°C) °C
Heat consumer
Distribution pipes 90 °C 45 °C
Radiator 70 °C 45 °C
Air heater 70 °C 45 °C
Reheater for air conditioning systems 50 °C 40 °C
Process heat Corresponding user demand
For new systems, the return temperature should always be designed as max. 45 °C
so that heat pumps and flue gas heat exchangers (condensing) can be used to in-
crease the return temperature (see diagram for central heat generation).
So as not to exceed the designed return temperature, the return temperature should be limited by electronic regulation or by regulators that do not depend on auxiliary
power.
4.2.2 Heat generation
Heat generation systems should be designed to DIN EN 12828.
Max. operating temperature 105 °C
Figure 4-5: Safety arrangement for heat generation systems to DIN EN 12828, op-erating temperatures up to 105 °C — example for direct heating
Key:
1 heat generator
2 shut-off valves supply/return
3 temperature controller
4 safety temperature limiter
5 temperature measurement sensor
6 safety valve
7 expansion trap ('T') > 300 kW 1) 2)
8 safety pressure limiter (max)
1), 1 > 300 kW
9 safety pressure limiter (min), as optional replacement for low-water protection
10 pressure sensor
11 low-water protection, up to 300 kW can also be replaced by an safety pressure limiter (min)
or flow rate monitor or other approved measures
12 filling connection, drain connection
13 automatic top-up
14 expansion pipe
15 protected shut-off valve
16 ventilation / emptying before expansion vessel
17 expansion vessel
1)not required
for indirect heating, if SV (7) for water outflow can be calculated
2)may be omitted if an additional safety temperature limiter and safety pressure limiter (max) are fitted
It is preferable to use condensing boilers. If the existing heat consumers were de-signed for high return temperatures, check whether at low load periods (spring, fall) the return temperature is sufficiently low that the low-load boiler can be fitted with a condensing heat exchanger.
Buderus boilers should be used, or Junkers boilers for small installations.
4.2.3 Standard circuits for heat generation and distribution
Figure 4-6: Outline diagram for central heat generation
1 boiler
2 condensing flue gas heat exchanger
3 heat pump condenser
4 heat recovery from compressed air compressor
Figure 4-7: Example heating diagram for building connection and consumer circuits
5.1 Electrically powered water heater for potable warm water generation in summer
d, e variable-speed pumps
A pressure differential of approx. 0.2 bar is maintained by the network pumps be-tween the flow and return distributors.
A bypass pipe with return temperature limiter is shown at the distributor so that flow is always maintained in the main pipe and hot water is immediately available when a control valve on the distributor is opened.
A valve with volumetric flow rate measurement equipment should be installed to
measure the heat quantity of the building. The flow and return temperatures are re-
corded by the building automation, and the heat quantity is calculated.
4.2.4 Heat consumers
4.2.4.1 Static heating surfaces
Static heating surfaces are mainly mounted along the facade. Large production halls with ventilation and extraction systems are only fitted with static heating surfaces in
special cases, e.g. workers seated directly at the facade.
If a ventilation system is fitted, the radiators should be designed for the transmission heating load. The ventilation heating load is covered by the ventilation system.
If the ventilation system is fitted with individual room regulation, i.e. the room tem-
perature is controlled by the ventilation system, the static heating surfaces provide
facade screening and are sized only for background heating (approx. 15 °C room
temperature).
Preferably compact plate radiators (Buderus Logatrend VK-Profil or VK-Plan) with
integral valves and thermostatic heads should be used. The radiators should be ar-
ranged so that partition walls can be built at the window axes. So as to restrict the
number of radiators, the radiator size is often chosen so that one radiator spans two windows.
Each radiator should be fitted with screw connectionswith shut-off function with a
drain cock in both the flow and return. The room temperature is usually regulated by means of the thermostatic valve.
4.2.4.2 Ceiling and wall air heaters, door air curtains
Draught preventers with a low volume of fork-lift traffic, and HGV docking stations with seals, should be provided with ceiling air heaters for rapid heating of the incoming cold air.
Draught preventers with a high volume of fork-lift traffic, and HGV docking stations
without seals, should be provided with door air curtains or air wall systems to reduce
the ingress of cold air.
In addition, ceiling and wall air heaters should also be used to heat storage areas and
simple production areas, and also for separate rooms such as technical areas.
To ensure rapid response behavior and to remain within the maximum return tem-
perature, the air heater circuits should be fitted with return temperature limiters that
do not depend on auxiliary power.
If a max. return temperature does not need to be ensured, a solenoid valve can also be fitted in each air heater circuit so that the hot water flow is interrupted whenever
the air heater is switched off.
4.2.4.3 Ventilation and air conditioning systems
In production areas with ventilation and extraction systems, the overall heating load is covered by the ventilation system. In office areas with ventilation and extraction
systems, the ventilation system covers only the ventilation heating load.
The supply air temperature is generally regulated by means of a mixing control
(constant flow, variable temperature). If accurate regulation is not required, and for
small systems, flow control can also be used (variable flow, constant temperature).
See below for circuit diagrams.
Figure 4-9: Connection and regulation of heating coils in air handling units.
Temperatures in main pipe 90°/45°C ?t = 45K
Temperatures for heating coil 1 70°/45°C ?t = 25K
Temperatures for heating coil 2 90°/45°C ?t = 45K
4.2.4.4 Process heat
If production equipment is supplied with heating, the max. permissible return tem-
perature should also be ensured by fitting return temperature limiters, so that the
network capacity can be optimally used.
If air compressors or production equipment are connected to the heating or process
heating network, and if there is a risk that oil or other substances can pass over into
the central heating circuit if there is a leak within the production equipment, the two
heating circuits should be separated by heat exchangers and an intermediate circuit, or by a safety heat exchanger.
4.3 Cooling supply with chilled water from chillers
4.3.1 Design temperatures for chilled water systems:
Inlet temperature Outlet temperature Chillers Chiller (standard) 12 °C 6 °C
Chiller if no dehumidification is re-
18 °C 12 °C
quired
Heat exchanger for free cooling 18 °C 12 °C
Cooling consumer
Distribution pipes 7 °C 13 °C
Air cooler for dehumidification 7 °C 13 °C
Air cooler without dehumidification 13 °C 18 °C
Chilled ceilings 16 °C 18 °C
Process cooling If possible 13 °C As high as possible
Feed temperatures at cooling consumers should be kept as high as possible so as
to obtain a good coefficient of performance at the chiller.
Particularly at process cooling consumers, the outlet temperature from the system
should be as high as possible, so that cooling tower water can be added to the cool-
ing medium, or used as the sole cooling medium for a large period of the year.
4.3.2 Chilled water generation
For generating chilled water, predominantly compression cooling machines with
scroll, screw or turbo compressors should be used.
Environmentally friendly refrigerants such as R 134a, R 410a, R 407c should be used.
When planning and designing the chilled water system, check whether feeding the
waste heat from the condenser into the heating system is practical and economic.
Figure 4-10: Outline diagram for central chilled water generation
Cooling systems with a small chilled water network should include a buffer vessel so as to avoid the chiller having to start and stop frequently.
At the heat exchangers for the cooling machines, the flow and return connections should each have a DN 50 shut-off butterfly valve or ball valve and a C-coupling, so as to permit a cleaning device to be connected to the heat exchanger without having to disconnect the main pipework.
So as to optimize the power consumption of chillers, chillers that supply both con-sumers with year-round demand, such as EDP recirculating air conditioning units, and also ventilation systems with dehumidification functions should be fitted with an external set point adjustment so that the cold water feed temperature can be raised from 6 °C to 12 °C during periods when no dehumidification is required.
For larger chillers, it is advisable to incorporate a balancing and measurement valve (e.g. KSB BOA-Control IMS) in the evaporator circuit to commission the volumetric flow rate at the specified rate and also to permit performance measurement.
Using the volumetric flow rate measurement and the flow and return temperatures, the building automation can calculate the heat quantity and with this value can opti-mize the corresponding activation of the cooling machines.
4.3.3 Cooling consumers
So that the chilled water pipework system is used to the optimum and the circulated water quantity is kept as small as possible, the returns from consumers with low
feed temperatures should be used to supply consumers with higher feed tempera-
tures. A circuit example is shown in the following diagram.
Figure 4-11: Connection diagrams for cooling consumers with different feed tem-
peratures.
4.3.3.1 Circuits for air coolers
─Option 1:
o Suitable for air dehumidification
o In larger air volume systems there is a risk of temperature layering
o Less expensive than option 2
─Option 2:
o Feed temperature in secondary circuit = feed temperature in primary
circuit
o Suitable for air dehumidification
o Little risk of temperature layering
o Primary pump does not have to overcome the pressure loss of the
cooling coil.
─Option 3:
o Feed temperature in secondary circuit > feed temperature in primary
circuit
o Suitable when the feed temperature at the cooler must be > network
feed temperature, e.g. recirculating air cooler
o If return water needs to be constantly mixed in, the control accuracy
is higher than for option 2
Figure 4-12: Control options for chilled water consumers
4.3.3.2 Circuits for process cooling
Process cooling consumers are mostly controlled by means of a two-port control
valve.
If process cooling consumers are not designed for the pressure of the primary net-
work, an indirect connection via a plate heat exchanger must be selected.
Indirect connections should also be used if there is a risk that in the event of a leak in the heat exchanger of the machining centre, the lubricant (oil, emulsion) may en-
ter the chilled water circuit.
With an indirect connection, the leak affects only the small intermediate circuit,
which can easily be monitored.
Figure 4-13: Diagram of a process cooling consumer
4.4Hydrauli c circuits für cooling tower systems
4.101 Open systems with 2 tanks
Cooling water temperature = wet bulb temperature + approx. 3K Temperature difference for chilled water circuit = 6 - 10K
In special cases higher values may be possible.