New options available for design of HVAC systems
The search for efficiency
Recent studies have shown that HVAC systems are responsible for 40% of the energy consumption of buildings and 17% of total energy consumption. Not to mention the fact that the growing demand for HVAC solutions from emerging countries will mean a probable increase in energy consumption. Hence the need for a truly efficient and sustainable vision of HVAC systems design emerges more and more urgently. In this sense, new technological solutions offer the opportunity to reduce plant management costs and CO2 emissions. However, this entails having to question established traditional approaches.
Alongside the designers
At Hecoclima, we have developed a series of innovative options aimed at reducing the general consumption of the system and at the possible reduction of installation costs, so that the end user can benefit from a return on investment in a shorter time. The energy efficiency of the entire system, in fact, is strictly influenced by direct savings in terms of electricity consumption and by solutions that seek to interpret the highest standards of plant design.
Variable primary flow systems
One of the innovations that is increasingly gaining ground in the hydronic air conditioning world are the variable primay flow (VPF) systems, which allow to reduce both installation costs and electricity consumption. Basically, compared to traditional systems consisting of two independent circuits, in a VPF system only one pumping group is used on the primary circuit to serve the entire system. This is made possible thanks to the technological evolution of control software that allow the refrigeration units to operate even in conditions of a variable water flow to the evaporator.
Variable flow on primary circuit
The new options available:
Pump with energy saving function
In the event of reduced refrigerant or thermal load and stopped compressors, the pump is also stopped, which is restarted periodically to check the thermal load conditions. This function can only be used in systems with primary circuit separated from the secondary circuit.
Variable speed and flow rate pump 70..100%
It can only be used in hydronic systems with primary circuit separated from the secondary circuit, it allows the regulation of the hydronic flow in proportion to the capacity supplied by the compressors.
Single pump, fixed flow on unit, variable flow on user circuit
The new options available:
Variable speed pump (inverter)
Additional option to the normal pump that can be used for the correct calibration of the delivery pressure – the primary circuit always remains at a constant flow rate at the value set on the electronic control, adjusting the speed of the pump to the variation of the pressure loss of the circuit.
Hydronic valve for bypass modulation
Manages variable flow on the system and constant flow on the unit, maximum manageable flow step 25% of the nominal flow rate. Can only be used with integrated pump and constant flow rate.
The advantages brought by VPF systems are considerable: the use of a single pumping group involves lower installation costs; the reduced number of components to be installed facilitates space optimization; the use of variable flow pumps eliminates pumping costs derived from the constant flow rate of traditional systems, in which the pumps are always running to bring water to the evaporator, even when it would not be needed; in VPF systems the pumping power required is lower, this means lower peak current and therefore the size of the electrical system can be reduced; finally, the VPF system allows to increase the water flow to the evaporator to values even higher than those of the project and in this way the ΔT remains constant.
… But under some conditions
All these advantages, however, can only be obtained by paying particular attention in the design phase to the selection of system components, their correct installation and the use of an advanced control system. It is true that traditional systems from this point of view require less care and are reliable even in the presence of poor maintenance. However, this should not be interpreted as a limitation of VPF systems, but as the opportunity to make a paradigm shift in the design of hydronic systems and in their management, where the quality of the components and their complete integration are the way to obtain a efficient system and tailor-made according to specific needs. This involves having an overview of the system, knowing the specific needs, selecting the components with an integrated approach and adequately training the dedicated staff.
The traditional approach can also have some advantages
Single pump, fixed flow system
Fixed flow on primary circuit + secondary circuit system
The traditional system, compatible with inverter pumps for a correct calibration of the curve, as seen above, however, allows to cover almost all the applications required by the market and to have an electrical energy consumption based on the actual working point of the pump.
Example: constant flow system with the use of an inverter pump for the calibration of the actual working point.
Note how in the example the use of a pump equipped with an inverter for calibration, even in a constant flow system, is able to optimize energy consumption and bring benefits to the machine and the system.
Point 1: fixed speed inverter pump correctly adjusted to the flow rate and head required by the circuit; minimal energy consumption
Point 2: fixed speed pump correctly adjusted to the flow rate and head required by the circuit by means of a balancing valve; energy consumption the greater the larger the pump
Point 3: fixed speed pump without circuit balancing: flow rate greater than the design point; maximum energy consumption, danger of pump motor overload, increased circuit noise, possible damage to the flow switch, possible excess flow alarm.
Traditionalists or innovators?
There are therefore also excellent reasons to continue designing hydronic systems as has always been done. For example, in cases where constant maintenance or precise adjustments cannot be guaranteed. Even in the case of installations of several chillers in series, in an industrial setting, the adoption of a VPF system becomes less convenient. However, it is undeniable that when conditions permit, this innovation allows to increase performance in terms of energy efficiency, with reduced costs and therefore ensuring a return on investment in a very short time. It should be considered an extra help for the designer who from time to time may prefer a more traditional and reliable solution or a more advanced system that requires a few more precautions, but immediately pays off both from an economic and environmental point of view.