As a heat network consultancy, we have a lot of experience in plant room control on both new build and legacy developments. As a result, we often see common control issues having large impacts on the efficiency and reliability of the heat supply.
These issues should be picked up at the commissioning stage via description of operation reviews and plant room demonstrations. Taking the plant room from minimum to peak load in a controlled load test is a key step to identify and rectify control issues that would otherwise only arise during occupancy.
Fortunately, a lot of the common control issues have simple solutions that can be implemented on the building management system Building Management System (BMS) panel to provide an instant boost to plant room performance. With the arrival of the heating season, there may be a number of easy alterations that can be made to reduce energy consumption and operating costs with robust controls solutions that ensure a consistent and low-cost supply to residents.
This blog piece will cover the most common plant room control issues and the simple BMS adjustments that developers and maintenance teams can make to rectify them.

The electricity consumption of pumps (both shunt and network) is a significant contributor to the ongoing operating costs of heat networks. Pumps are commonly found operating ‘in hand’ or with a fixed speed setting – leading to pumps constantly running at high speeds regardless of the system load.
There are four main operating modes for pumps they are, in order of least to most efficient:

Adjusting the pump control methodology down this list is a very quick way to significantly reduce pump electricity consumption – especially if index run control is possible. It is essential when selecting a differential pressure control method that the correct set point is selected, providing further reductions in electricity consumption. Furthermore, reduction in pump speeds at low system loads can enable the closure of network bypasses, reducing return temperature and further reducing pump energy consumption.Proposals on recent site audits have enabled pump energy reductions of over 90% by changing from a fixed speed approach to an index run approach.

Boilers are often incorrectly sequenced, leading to high boiler run hours, high gas consumption and poor consistency of heat delivery to residents.
To avoid these issues a complete boiler sequencing methodology should be implemented, utilising thermal store temperature sensors where possible, with regular rotation of the lead boiler. This will reduce wear on all boilers and significantly increase the efficiency and consistency of supply. Whilst this is likely to require a Building Management System (BMS) engineer to implement, the savings far outweigh the low initial costs.
An example of the difference between the flow temperature stability on a site with a 72 °C set point before and after BMS works to rectify boiler sequencing can be seen below.

The constant cycling of the boilers seen before the works was significantly increasing the wear of the boilers – leading to early failure and increased maintenance costs. Furthermore, the large variations in flow temperature would make it difficult to reduce network flow temperatures in the future without causing issues with the supply of heating and hot water to dwellings.

Control over the operation of PHEs can have a huge impact on plant room return temperatures and, thus, generation efficiency. A well performing network with low return temperatures (c. 30-40 °C) can still have high plant room return temperatures, leading to boiler inefficiency and high pump energy consumption if PHE control is implemented poorly.
Usually, the best way to control a PHE is to control the primary flow rate with a control valve on the primary side to maintain a secondary flow temperature set point. However, on occasion the control valves are left wide open or controlled poorly, causing the PHEs to act as high flow rate bypasses within the plant room.
An example of this can be seen in the graphs below, where a 206-unit residential scheme in poplar was experiencing high primary return temperature despite a well performing secondary system. In this example the set point for the secondary flow temperature had been set to the same value as the primary flow temperature set point, thus any fluctuation in primary flow temperature caused the PHE control valve to open completely and pass very high flow rates through the PHE. The second graph shows the same system after a reduction in secondary flow temperature set point, enabling consistently low primary return temperatures representative of the network performance.

Implementing a defined control strategy for each piece of equipment can only be realised if the BMS data is well structured and clearly organised.
Since issues with the controls logic can arise during original commissioning or as a result of subsequent maintenance alterations, it’s crucial that the current performance of the system is visible and can always be understood. Consequently, we would recommend the following housekeeping principles to ensure the security and visibility of BMS systems:

Addressing simple BMS changes such as the above can have a huge impact on energy consumption, carbon emissions, heat costs and resident satisfaction.
Issues such as the above can be avoided entirely by proper design and commissioning at the build stage. From personal experience, we have found that a full DesOps review and plant room demonstration (including load tests) are crucial to ensure compliance with the design intent and maximising the efficiency of the installed equipment.
If you have any other control tips or examples where controls changes had a big impact on system performance, please comment below or drop us a message to discuss.