Follow Inta’s experts guide to Heat Networks and find out about how they are designed, built and optimised
Schematics, drawings and example figures do not constitute an actual design, and each project should be reviewed individually as a unique design process.
Note 1 (Ref G in the drawing).
The reverse acting differential pressure controller (RADPCV) is sensing the pressure differential between flow and return riser pipes as the HIU control valves close down, the head pressure will increase causing the increase in the pressure difference between flow and return pipes. When there is no demand from the HIUs, then this valve provides the alternative flow path. The valve opens to compensate, and bypasses the flow into the return bringing the pressure difference back to the set value. The valve will continually modulate the pressure differential. In most cases, the valve is set to control a value about 10% above the operating point of the system at the design conditions.
Schematics, drawings and example figures do not constitute an actual design, and each project should be reviewed individually as a unique design process.
As described in the CIBSE CP1 Heat networks code of practice.
Note 2 (Ref D in the drawing).
The Substation separates the buildings from the district heating pipe network or used as a pressure break in very high building to prevent extreme pressure differentials. Where the temperatures and pressures of the building’s heating systems differ from those of the district heating network, it is usually necessary to utilise a Substation. A Substation consists of a plate heat exchanger which creates pressure break between the district network and consumer system. The district heating supplier will provide information on the actual minimum and maximum differential pressures, as measured at the service connection valves. This data should be used for determining the sizes and capacities of control valves and heat exchangers.
As described in the CIBSE CP1 Heat networks code of practice.
District heating networks in some cases can cover large areas and service multiple buildings and homes. They can be added to later and also linked to other schemes to form an even larger network. As such it is important that the M&E consultants and Developers understand where the key lines of responsibility lie.
Demarcation and ownership is important and should be clear to ensure that the responsibility for maintenance and metering understood by all involved. Demarcation is important for small community heating schemes as well as larger networks.
Centralised plant rooms in large buildings and separate substations for smaller buildings are recommended. The plate heat exchangers in these plant rooms and substations create clear demarcation lines that separate the main network from each individual building or estate, and providing a pressure break.
Pressure breaks in communal heating plant rooms and substations ensure that taller buildings do not affect the pressure in
other parts of the network.
The design engineer will be looking to achieve the most efficient source of heat that is practical for each individual project. Gas condensing boilers, multi stage boilers, heat pumps, and to a lesser degree combined heat and power (CHP) or biomass boilers. Other low carbon methods such as solar thermal are also to be considered as secondary heat sources. Larger systems can tap into waste heat recovery projects.
Usually a twin pump set for circulating water and heat from the heat source to the buffer tank at constant speed / flow.
The pump will be moving heat from the heat source and into the buffer as required.
The purpose of the buffer vessel is to provide heat to meet peaks of maximum demand which occur over short periods,
storing heat for later use and supplementing the heat source when demand is high. Stored heat is immediately available
without the heat source needing to get up to temperature. The buffer should be sized correctly to match the load demand
with consideration to the heat source, building construction, and even the number of people that possibly can create a
demand during peak demand times, usually morning and evening.
Variable speed circulating pump capable of efficiently operating at operating at part load. The pump should be sized to meet
speed and flow design requirements and be controlled so that there is always sufficient pressure and flow available to feed all
the HIUs in the network equally.
Provision for venting air from the Risers, Provision for maintaining circulation when all control valves in the HIUs are closed.
Schematics, drawings and example figures do not constitute an actual design, and each project should be reviewed individually as a unique design process.
Shower 7.75 L/min (70% HW) | Shower 9 L/min (70% HW) | Basin 6 L/min (70% HW) | Basin 4 L/min (70% HW) | Kitchen Sink 6 L/ min (100% HW) | Bath 12 L/min (70% HW) | Bath 12 L/min (70% HW) | Power |
---|---|---|---|---|---|---|---|
Ltr/hr | Ltr/hr | Ltr/hr | Ltr/hr | Ltr/hr | Ltr/hr | Ltr/hr | kW |
325.5 | 378 | 216 | 168 | 360 | 504 | ||
outlets in use simultaneously – flow rate in ltr/hr | |||||||
OFF | 378 | OFF | OFF | OFF | OFF | 378 | 19.8 kW |
325.5 | OFF | OFF | OFF | 360 | OFF | 685.5 | 35.9 kW |
OFF | OFF | OFF | 360 | OFF | 738* | 38.6 kW | |
OFF | OFF | OFF | OFF | 360 | 504 | 864 | 45.2 kW |
Shower 7.75 L/min (70% HW) Ensuite shower | Shower 9 L/min (70% HW) Main shower | Basin 6 L/min (70% HW) | Basin 4 L/min (70% HW) | Kitchen Sink 6 L/ min (100% HW) | Bath 12 L/min (70% HW) | Total flow in required for heating to hot water | Power |
---|---|---|---|---|---|---|---|
325.5 | 378 | 216 | 168 | 360 | 504 | l/h | kW |
outlets in use simultaneously – flow rate in L/h | |||||||
OFF | 378 | OFF | OFF | OFF | 378 | 17.6 kW | |
325.5 | OFF | OFF | OFF | 360 | OFF | 685.5 | 31.9 kW |
OFF | 378 | OFF | OFF | 360 | OFF | 738* | 34.3 kW |
OFF | OFF | OFF | OFF | 360 | 504 | 864 | 40.1 kW |
OFF | 378 | OFF | 168 | 360 | OFF | 906 | 42.1 kW |
Outlet | Design flow rate 1 | Minimum flow rate 2 | Supply temperature °C 3 | ||
---|---|---|---|---|---|
L/sec | (L/min) | L/sec | (L/min) | ||
Bath (from storage) | 0.30 | (18) | 0.15 | (9) | 48 |
Bath (from combi) | 0.20 | (12) | 0.15 | (9) | 40 |
Shower (non-electric) | 0.20 | (12) | 0.10 | (6) | 40 |
Wash basin | 0.15 | (9) | 0.10 | (6) | 40 |
Sink | 0.20 | (12) | 0.10 | (6) | 55 |
Shower 9 L/min 100% hot water | Basin 6 L/min 100% hot water | Kitchen Sink 12 L/min 100% hot water | Bath 12 l/min 100% hot flow | Total flow in ltr/hr hot water requirement | Power kW |
---|---|---|---|---|---|
540 Ltr/hr | 360 Ltr/hr | 720 Ltr/hr | 720 Ltr/hr | ||
540 | 540 | 28.25 kW | |||
720 | 720 | 37.67 kW | |||
540 | 720 | 1260 | 65.9 kW | ||
720 | 720 | 1440 | 75.34 kW |
Shower 9 L/min 85% mixed hot water | Basin 6 L/min 85% mixed hot water | Kitchen Sink 12 L/min 85% mixed hot water | Bath 12 l/min 85% mixed hot water | Total flow in ltr/hr mixed hot water | Power kW |
---|---|---|---|---|---|
459 Ltr/hr | 306 Ltr/hr | 612 Ltr/hr | 612 Ltr/hr | ||
459 | 459 | 20.28 kW | |||
612 | 612 | 27.04 kW | |||
459 | 612 | 1071 | 47.32 kW | ||
459 | 306 | 612 | 1377 | 60.84 kW | |
612 | 612 | 1244 | 54.08 kW |
Qty HIU | DHW Load (kW) | Factored loadper HIU | Max Power per HIU | Coincidence Factor |
---|---|---|---|---|
1 | 37.6 | 37.6 | 37.59 | 100% |
2 | 46.6 | 23.3 | 75.18 | 61.94% |
3 | 53.7 | 17.9 | 112.77 | 47.65% |
4 | 60 | 15 | 150.36 | 39.88% |
5 | 65.6 | 13.1 | 187.95 | 34.90% |
6 | 70.8 | 11.8 | 225.54 | 31.39% |
7 | 75.7 | 10.8 | 263.13 | 28.76% |
8 | 80.3 | 10 | 300.72 | 26.70% |
9 | 84.7 | 9.4 | 338.31 | 25.04% |
10 | 89 | 8.9 | 375.9 | 23.66% |
11 | 93 | 8.5 | 413.49 | 22.50% |
12 | 97 | 8.1 | 451.08 | 21.51% |
13 | 100.9 | 7.8 | 488.67 | 20.64% |
14 | 104.6 | 7.5 | 526.26 | 19.88% |
15 | 108.3 | 7.2 | 563.85 | 19.20% |
16 | 111.8 | 7 | 601.44 | 18.60% |
17 | 115.3 | 6.8 | 639.03 | 18.05% |
18 | 118.8 | 6.6 | 676.62 | 17.56% |
19 | 122.2 | 6.4 | 714.21 | 17.10% |
20 | 125.5 | 6.3 | 751.8 | 16.69% |
25 | 141.4 | 5.7 | 939.75 | 15.04% |
30 | 156.3 | 5.2 | 1127.7 | 13.86% |
35 | 170.5 | 4.9 | 1315.65 | 12.96% |
40 | 184.1 | 4.6 | 1503.6 | 12.24% |
45 | 197.3 | 4.4 | 1691.55 | 11.66% |
50 | 210 | 4.2 | 1879.5 | 11.18% |
60 | 234.6 | 3.9 | 2255.4 | 10.40% |
70 | 258.2 | 3.7 | 2631.3 | 9.81% |
85 | 292.1 | 3.4 | 3195.15 | 9.14% |
90 | 303.1 | 3.4 | 3383.1 | 8.96% |
100 | 324.6 | 3.2 | 3759 | 8.64% |
110 | 345.7 | 3.1 | 4134.9 | 8.36% |
120 | 366.3 | 3.1 | 4510.8 | 8.12% |
130 | 386.7 | 3 | 4886.7 | 7.91% |
147 | 420.5 | 2.9 | 5525.73 | 7.61% |
150 | 426.4 | 2.8 | 5638.5 | 7.56% |
175 | 474.6 | 2.7 | 6578.25 | 7.21% |
200 | 521.5 | 2.6 | 7518 | 6.94% |
250 | 612.4 | 2.4 | 9397.5 | 6.52% |
337 | 763.8 | 2.3 | 12667.83 | 6.03% |
400 | 869.6 | 2.2 | 15036 | 5.78% |
500 | 1033 | 2.1 | 18795 | 5.50% |
1000 | 1802.1 | 1.8 | 37590 | 4.79% |
10000 | 13797.6 | 1.4 | 375900 | 3.67% |
The likelihood of everybody opening all their taps and using their showers at the same time is extremely remote, in fact, it would never happen. So as mentioned before, system designs incorporate this into their pipework sizing. Over-sizing has obvious disadvantages in increased capital costs, as well as increased network heat loss. For Risers, the effect of over oversizing vertical pipes is less critical, air and dirt can be easily eliminated, and low temperatures on the return riser pipework limits heat loss issues. In general, sizing with a ‘safety’ factor to allow for unknowns reduces thermal efficiency.
Applying the co-incidence factor allows each section of pipework to be sized in accordance to its position in the network, and the peak loads it will have to carry. For this example we choose the 37.6 kW as in the Danish DS439 table.
Schematics, drawings and example figures do not constitute an actual design, and each project should be reviewed individually as a unique design process.