The role of pumps in district energy systems
Go behind the scenes and learn why pumps are the beating heart of district energy.
District energy is an energy-efficient solution and, if applied correctly, it can also be the most sustainable. But how does it actually work? And how is the energy transported from A to Z? For a start, a number of pumps work together to contribute to a successful district energy system. They ensure that water gets from the central plant to individual homes in the most energy-efficient and reliable way.
In this module, we’ll use a combined heat and power plant – also known as a CHP power plant – as our point of departure. We’ll break down the step-by-step process of how a number of pumps transform energy into heated or chilled water. Along the way, we will examine every step, highlighting the significance of every pump.
Let’s start at the aforementioned CHP power plant. From here, district energy is produced by means of fuels such as biomass, solar energy and wind energy among others. This process kick-starts the water’s journey toward domestic homes and industrial buildings. Once water is pumped out to sub-stations, it’s finally ready to be distributed to households to control indoor temperatures and heat water.
While this example highlights how energy is produced at a combined heat and power plant, the process of a district energy system is essentially the same regardless of the type of power plant you are dealing with. Every pump along the way is a crucial cog in the machinery that is a district energy system. Together, the pumps ensure that district energy is the most sustainable, energy-efficient and cost-effective solution to energy challenges. And it all starts at the central plant.
The main pumps at these plants are the heartbeat of district energy systems. Their objective is to distribute vast amounts of water to the distribution system. Due to the length of the water’s journey, it is essential that they’re built sturdily and reliably in order to last as long as possible. Before water is distributed, it’s crucial that the quality lives up to the given standards. In order to guarantee this, it must be filtered on an ongoing basis. Flow filter pumps recirculate approximately 10% of the total flow through a strainer.
A strainer is typically located near control valves and helps remove impurities such as debris and other materials that may enter the pipes. Removing impurities is critical, as it prevents any reductions in system efficiency.
Boiler shunt pumps maintain the performance of the system by recirculating the water in the boiler. In that way, the pumps ensure that the difference in temperature between the top and bottom of the boiler isn’t too high. This reduces condensation risk, which is crucial for boilers that aren’t designed to withstand condensation. At worst, condensation can cause corrosion and result in a reduced system lifetime. A boiler shunt pump helps bypass these issues, which ultimately leads to a much longer lifetime.
Lull heat pumps ensure a quick start-up and an optimal protection of boilers. They provide a steady flow of water through the boiler even when it’s on standby. And in doing so, the system can restart promptly without having to reheat the water first.
Flue gas temperature can considerably influence the overall efficiency of a boiler. Installing an economiser between the boiler and chimney allows it to control the boiler’s flue gas. This ensures that any absorbed energy is put to good use. Installing a flue gas economiser can reduce fuel costs by 15-25% depending on plant type and fuel selection.
At this stage, the water we’ve followed from the central plant is on the home stretch. Distribution pumps transport water from sub-stations to individual consumers and before you know it, radiators are filled with hot water and household temperatures can be regulated.
In order to reach remote areas, pumps can also be distributed further in the system. By installing mixing loops, this can also reduce system pressure. The Grundfos iGRID Temperature Zone is an intelligent mixing loop that enables delivery of the exact temperatures required. By dividing the city into smaller zones where demands are lower, temperatures are reduced to a given setpoint or on-demand by mixing return water into the supply line to reach the needed supply temperature for the zone. Connected to iGRID Measure Points, temperature optimisation is based on real-time data from strategic points in the grid. With iGRID Temperature Optimiser added, the optimal supply temperature setting for the district heating grid is calculated. This reduces peak load flow rates (Peak Shaving) and compensates for actual weather conditions. In this way, iGRID controls the flow and temperature of the District Heating to meet different consumers’ temperature demands as well as utilise sustainable energy sources in certain areas of the network.
All these phases combine to make up a successful district energy system, while distinctly highlighting why district energy is the energy solution of the future. Let’s go through the features and benefits of each pump one last time:
Main pump: Distributes water to the distribution centrals.
Boiler shunt pump: Recirculates water and reduces condensation.
Flow filter pump: Removes all impurities from recirculated water.
Lull heat pump: Ensures quick start-up and optimal protection of the boiler.
Flue gas economiser: Cools the flue gas reducing fuel cost by up to 15-25%.
Distribution pump: Distributes energy to individual homes.
iGRID pumps distributed further out in the system to meet different consumer requirements.