Energy efficiency in buildings is more important than ever. To optimise the efficiency of a solution for ventilation, heating and cooling (HVAC) and also maintain high comfort levels, considerations can not only be made to the efficiency of individual units, they all need to work together.
Energy efficiency has for long been an area of interest in the building sector. It is well known that the topic of energy efficiency has become more urgent in recent years. The need to fight climate change is one cause, the rapid increase in energy prices another. EU plan for the green transition called “Fit for 55”, which aims to reduce greenhouse gas emissions by at least 55 percent by 2030. As part of the plan, the Energy Performance of Buildings Directive (EPBD), targets a 55 percent energy reduction in buildings by 2030, as well as a fully decarbonised, zero-emission, building stock by the year of 2050. To get there, all new public buildings must accomplish zero-emission already by 2027. Hence, there are strict requirements in place in regards to energy efficiency of HVAC equipment used in both new buildings as well as in renovation projects.
Energy savings can be achieved at a number of points within a building, in scales from the smallest, individual components and user settings, to the largest, system level solutions. Let’s walk through it.
An initial look at heat pumps
- Lower heating temperature. The most immediate and effective way to increase efficiency is to decrease the heating set point. Radiating floors and ceilings, fan coils and traditional radiators all work at different temperatures. Low temperature terminals must be preferred, but if stuck with high temperature terminals, increase the exchange surfaces in order to lower the working temperature setpoint.
- Dimension heat pump properly. A heat pump should be sized to the needed capacity. Generally, heat pumps are oversized because they are selected for the worst ever operational conditions. In that case, the units will be working inefficiently, with an extremely low load. Try not to oversize.
- Use an inverter compressor. An inverter compressor in a heat pump will help to regulate the load, which results in higher stability and efficiency of the plant as a whole. For high thermal capacities, a multicircuit multiscroll unit can fit as well.
- Consider the seasonal load. Heat pump loads can vary greatly depending on the season. Base the choice of heat pump on the seasonal efficiency (SCOP) of the installation latitude – not the full load efficiency.
In summary, it is extremely important to select proper units, and to use relevant settings. Tweaking these parameters can save a lot of energy without compromising the Indoor Environmental Quality.
Efficiency of plants with multiple heat pumps
But there is more to be done – the overall efficiency of the plant should also be considered, in particular in plants with multiple heat pump units.
- Balance multiple units. In a plant with multiple units, the efficiency of the individual units matter. However, the control system and how heating capacity requests are distributed across the plant is vital to carefully consider, this will influence the overall efficiency greatly. It is important to use a distributed intelligence that automatically optimises activations and loads in order to maximize the efficiency.
- Defrost smarter. In a system of multiple air source heat pumps, the defrosting process can be a tremendous waste of energy if not well managed. A distributed intelligence can minimise the frequency and duration of defrosts and increase the stability of the plant. Remember, an unstable plant is an inefficient plant.
- Implement variable water distribution. The hydronic system can be optimised in many ways, for instance by adding inverters to modulate the water flow. An even better way forward, is to consider a smart control system which uses dedicated temperature or pressure sensors to regulate the water flow in accordance with the actual load of the plant. A system like this can easily save up to 50% of the energy for pumping compared to a system with a constant flow. Even more critical in a solution of multiple units with a single centralised pump. Without variable water flow control, a significant amount of water might be recirculated, which results in a huge energy waste.
- Adjust the setpoint. Using smart regulation that compensate the heat pump set point working value can improve energy efficiency. This is possible for a single unit, as a function of the external temperature for instance. In a multiple, smart and connected system the heat pump set point can be regulated according to real time conditions of the plant and not only to the external temperature, and also to room occupancy, day of the week and solar radiation, as an example.
Ideally the entire HVAC system of a building should interact in order to ensure maximum comfort with minimal energy consumption. I see the HVAC components in a solution as a gathering of musicians, an orchestra, where each unit is an expert of its own. However, to perform beautifully together, an orchestra conductor is needed. Our Swegon optimisation system is the orchestra conductor, which ensure that all components work together in a harmonised orchestra.