Putney Plaza Manual
THE DESIGNS INCORPORATED INTO THE PUTNEY PLAZA SYSTEM ARE COVERED BY 3 SEPARATE PATENTS.
- 1 Overview
- 2 Photographs
- 3 Monitoring
- 4 Plantroom Schematic
- 5 Buffer Cylinders
- 6 PHE Modules
- 7 Schedule of Control Valves and Settings
- 8 Network
- 9 Controls Logic
- 9.1 Controller IDs
- 9.2 Storage Controller
- 9.3 Boiler Return Controller
- 9.4 Module Controllers
The Putney Plaza Energy Centre supplies hot water and central heating to multiple dwellings and commercial properties. A combination of gas boilers, CHP, and Extract Air Heat Pumps are used to provide heat.
The heat pumps heat central heating water returning from properties, by extracting energy from waste air from ventilation. The heat pumps will however only achieve limited temperatures, and if required the energy centre tops up the temperatures using stored energy, before it is sent back out to properties.
The energy centre makes use of two sets of heat store, with one bank of stores held by boilers and CHP at high temperatures, and the second bank holding lower temperature water.
The system comprises of:
- Central boilers, both CHP and gas, with return temperature mixing valves
- 8000 litres central buffer storage for boilers (high grade storage)
- 8000 litres central storage of returned heat (low grade storage)
- 4 Output zones
- Domestic hot water
- Central heating (radiators)
- Central heating (underfloor)
- Commercial units
- Each zone is fitted with an extract air heat pump, heating the return from the zone to the plant
- Modular plate heat exchanger sets used to drive loads in addition to heat pumps, drawing heat from both the high grade and the low grade storage
The system logs all sensor data to a web server for viewing online.
Graphs for commission date 16/6/2015
The scheme requires two banks of 8000 litres of storage. This can be provided by a combination of eight individual 2000 litre buffer stores.
- Make: Flamco
- Model: PS2000
- Material: Mild Steel to ASTM/ISO: A181
- class 60 / S235JRG2, EN/ISO: P245N
- Height: 2350mm
- Diameter: 1100mm + (2x 100mm
- Insulation) = 1300mm
- Weight (Empty): 284 Kg
- Working Pressure: 3 Bar
- Test Pressure: 4.2 Bar
Connections are customised for this contract and will provide 2 x 3” *connections per store (top and bottom) as well as 3 x ¾” connections for sensors, and base connection for drain point.
Modular connection of units allows very high outputs to be achieved. This approach has the following advantages:
- To maintain operation under failure, one needs a standby exchange set, possibly doubling costs if using heat exchanger sets sized to duty. Smaller modules allow a better level of standby protection without significant standby provision (one small module).
- Multiple levels of redundancy allow near peak system performance to be maintained with one or more component failures.
- With three or more modules, one achieves ‘triple redundancy’. With only one standby module, when there is a sensor error (such as system pressure) it is often difficult or impossible to ascertain which reading is accurate. With three modules, a sensor failure can always be isolated as its value is compared to at least two other accurate sensors.
- Not only is there redundancy in heat exchangers and pumps, but also in controls, with each unit having its own electronics. Units will talk to each other and can report the status of other modules as well as work together to achieve optimum system performance.
- Modules can be individually isolated and serviced.
- Domestic sized controls, pumps and heat exchangers keep spares prices down, and are easy to handle and replace, with less water to drain.
- Small heat exchangers are easy to flush.
- Assemblies are easily wall mounted onto main pipework, requiring a smaller footprint in plant rooms than larger floor mounted heat exchange sets.
- Complete systems can optionally be cased, reducing the need for large amounts of site applied insulation.
- Low loads can be met by pulsing pumps in turn.
- Option for WRAS approved full bore motorised isolation on DHW side of each set allows it to automatically shut down in failure mode. This prevents it from acting as a bypass, allowing cold water through to the outlet manifold. Very low loads can also be met with this option
Heat Exchanger Duties
Heat Exchanger Sets
Schedule of Control Valves and Settings
Two control valves are used within the boiler circuit to mix a portion of the boiler flow into the return to maintain return temperatures. This is to avoid the generation of water as temperatures below setpoints, and to protect boilers from water that is too cold.
The valves are each controlled by a dedicated control box (see below) that are connected to the system network.
The setpoint for the valves is 55°C, based on boiler peak efficiency operating temperatures of 55 to 75°C.
All controllers are connected on a local area network (LAN), with the ability to communicate. If an internet connection is available the will log data to the internet, send alarms via email, and allow remote setup.
The system makes use of ESW 500 Ethernet Switches for establishing a LAN.
The system uses a Conel UR5i v2 Libratum GSM Router to provide internet connectivity, and to act as the DHCP server for the LAN.
The IP adresses for the network modules is 192.168.1.1 - 192.168.1.20.
The controls are split into 3 separate zones.
- Storage Controller - reads temperatures in stores and brings in boilers in sequence. There are effectively two boilers - the CHP unit as the lead, and the gas boilers as assist.
- Boiler Return Controller - modulates the recirculation of heated water from boilers back the return to prevent temperatures dropping below the design point. There are two of these controllers to provide redundancy.
- Module Controllers - fitted to each heat exchanger module to control generation of hot water to loads.
Each module has a serial number used to register it within the network, and onto the online databases. These are as follows:
|Boiler Valve Controllers||29, 30|
|Radiator Modules||32, 33|
|UFH Modules||34, 35, 36|
|Commercial Modules||37, 38|
|DHW Modules||39, 40, 41, 42, 43, 44|
The storage controller connects to a temperature sensor in each of the four high temperature buffer stores, as well as a sensor on the input and output from the storage set. Store 1, is nearest to the return, with store 4 been on the hot output.
The installation is fitted with RPS Temperature And Pressure Sensors.
- CHP turned on when both store output and store 4 below 65°C.
- CHP turned off when both store output and store 4 above 70°C.
- GAS BOILERS turned on when both store 4 and store 3 below 65°C.
- GAS BOILERS turned on when both store 4 and store 3 above 70°C.
Note set temperatures are adjustable.
The following dashboard interface is provided for the Storage Controller.
Boiler Return Controller
The return ‘loading’ valves are three-point control (power open, power close) with a temperature sensor mounted into the output pipework. Valves have stroke of 20mm, and actuators run at 7.5s/mm, giving total open/close time of 150s. There is a 2 degree dead-band.
The installation is fitted with an RPS Temperature And Pressure Sensor on the valve output.
- VALVE OPENS (increase temp) when output temperature drops 2°C below setpoint.
- VALVE CLOSES (reduce temp) when output temperature rises 2°C above setpoint.
- Setpoint Temperature 55°C
- Deadband 2°C
The module controllers make use of a speed controlled primary pump, and two motorised valves (three point control) to control:
- The flow of secondary heated water through the unit. The flow is shut down when a module is off or in standby.
- The temperature of primary water fed to the heat exchangers, drawing from a high and a low temperature storage.
- The flow rate of primary water into the heat exchanger set.
Preference is given to the low temperature heat source, with the modules drawing on the high temperature supply as load increases. In the case of the commercial and radiator circuits, flow temperatures will always be fixed higher than the low temperature source, so are not connected to the low temperature source.
The modules are fitted with temperature sensors on all four ports (primary/secondary in/out), flow sensors on each circuit, and pressure sensors on each circuit.
The flow sensors are used to detect secondary flow (and hence load) and will initiate the supply of primary water using the circulating pump.
Heat Source Selection
On modules with two heat sources, temperature is initially controlled to target load temperature +2°C, and pump flow rates are ramped up to achieve target. If target temperatures cannot be achieved at this supply temperature, (indicated by pump speed increasing to 75% duty, or 130% of secondary flow), the supply temperatures are increased to achieve target.
On modules with one heat source, temperature is controlled by modulating pump speed. If the load is too low for pump, then primary valve will modulate down, to adjust point on pump curves.
Additional Module Functionality
Where more than one module is used, the modules communicate with each other to determine:
- the total load
- the number of modules required to achieve load
- which modules are to operate - modules are rotated for even use
Modules that are surplus to load requirements are shut down, and the secondary flow is closed off. This is to ensure that at low loads, flow rates through modules in use is maintained at a level to achieve turbulent flow, and design heat exchange.
Modules in communication with each other determine a master that calls slave units into play as required. If a module cannot communicate with another module is assumes the role of master and will always run.
The master will perform the function of weather compensation if required. Outside air temperatures are determined from connection to online weather data. If internet communication is down, the system will use the same outside reading as the same hour on the previous days, adjusted by temperature at time of loss of coms.
Modules connected to the low temperature heat source (UFH) have the ability to draw heat generated by the waste air heat pumps into the low temperature storage. Where the secondary return temperature increases above the low temperature storage, stored water will be circulated through the module to extract heat.
As the system is not using a secondary DHW recirculation system, it is anticipated that there will be very low loads, and times of no load, and no flow. The lead DHW module will always maintain circulation primary circulation of 15 lpm at the DHW setpoint in order to satisfy secondary flows too low to detect (<10 lpm).