Blowing hot and cold
Two recent projects in Milan illustrate the benefits of using multi-purpose simultaneous heating and cooling units for four-pipe fan coil systems. Dean Ward, Applied Products Manager with Climaveneta UK, explains.
Earlier this year a new building in the Vimercate Energy Park in Milan was the first building in Italy to achieve the LEED Platinum Core & Shell 2.0 certification. One of the reasons for this was the approach the designers took to ensure that simultaneous heating and cooling could be provided to different parts of the building without the energy wastage that is found in many other buildings.
The technology employed in this project has resonance for many projects in the UK, as it addresses energy efficiency issues that are common to many commercial buildings.
Early on in the design stage at Vimercate, energy modelling indicated that there would be a need for heating and cooling at the same time in different parts of the building, due to variable internal heat gains and changing solar orientation. Traditionally, this could be addressed by using a four-pipe fan coil system served by separate boilers and chillers. The problem with this is that while the chillers are generating chilled water and rejecting heat to the outside, the boilers are generating heat for other parts of the building. This is clearly wasteful of energy.
As a more energy efficient alternative, M&E designers Lombardini 22 selected Climaveneta’s Integra multi-purpose – sometimes known as polyvalent – units. These are able to generate hot and cold water simultaneously, without seasonal switching. Crucially, the heat generated by the production of chilled water can be used for heating, and vice versa, resulting in typical energy savings of around 40% compared to using separate boiler and chiller plant.
For further energy savings, the units at Vimercate Energy Park have been combined with a heat exchange system that uses groundwater as the external heat source. To minimise environmental impact this system incorporates a ‘water save’ function that reduces the water flow rate to the heat exchanger in proportion to the use of the system. In this way the energy required for pumping is minimised, as are the discharge costs for the drained water.
For the Segreen Business Park, an LEED Gold urban renovation project in Milan, Lombardini 22 have used the Integra units again, but in a different configuration. As with the Vimercate Energy Park project, heating and cooling is via a four-pipe fan coil system and the two Integra units are able to provide simultaneous heating and cooling, using groundwater as a heat exchange medium. The difference here is that one unit works as an air condenser and the other as a water condenser.
Roberto Cereda of Lombardini 22 says: “The main advantage of polyvalent units lies in the fact that they are able to satisfy the demand for hot and cold water simultaneously through a system that does not require seasonal switching, and is therefore a valid alternative to traditional plants of chillers and boilers.”
As well as reducing energy consumption and ensuring a highly responsive system, the use of multi-purpose units also brings additional cost of ownership benefits. Installation requirements are reduced as there is only one unit to connect and commission, and they also free up plant room space as a multi-purpose unit has a smaller footprint than chiller and boiler plant.
How it works
Designed specifically for use with four-pipe hydronic systems, Climaveneta Integra units differ from traditional reverse cycle heat pumps, in that they are divided into two separate sections; one hot (condenser side) and one cold (evaporator side). As mentioned earlier, they can produce hot and chilled water at the same time and totally independently, adapting to variable demands from different parts of the building.
Typically the units will be specified on the basis of the maximum predicted peak demands for hot and chilled water. This means that for much of the year they will be running at part-load so it is important to design for maximum part-load efficiency. To that end it makes sense to opt for units with inverter control of the compressors.
There are three basic operating configurations, which are totally independent of external temperatures – chilled water only, hot water only and combined production of hot and chilled water.
In a chilled water only configuration the unit works like a simple chiller and therefore rejects the condensation heat to the atmosphere through an air-refrigerant finned tube heat exchanger (condensation coil). The water is cooled in a refrigerant-water exchanger (evaporator).
In the hot water only configuration the unit works exactly like a heat pump, channelling the heat extracted from outdoor air through an air-refrigerant finned coil (evaporator) in order to heat the water being distributed around the building through a refrigerant-water exchanger (condenser).
The main difference compared to traditional reverse cycle heat pumps is that the hot water is produced in a different heat exchanger to that used for the production of chilled water, thanks to the use of a dedicated evaporator. This is vital in maintaining the separation of hot and cold sections.
When hot and chilled water are required at the same time the unit behaves like a water-water unit, managing condensation and evaporation on two separate heat exchangers connected to the two separate circuits (hot and chilled) of the four-pipe system. The heating and cooling energy are provided respectively to the condenser and evaporator. These heat exchangers are then hydraulically coupled to the two circuits of the system.
The control logic developed specifically for these units ensures that they are always able to respond to building loads. The two refrigerant circuits are managed intelligently by the unit’s controller and are able to adapt independently of each other to meet building loads with optimum efficiency.
The use of suitable thermal storage tanks on both hot and cold sides helps to provide effective system operating modularity and minimises running costs.
With a unit that provides heating and cooling simultaneously, the traditional ratings such as Coefficient of Performance and Energy Efficiency Ratio become less meaningful. Consequently, Climaveneta has developed an alternative to objectively measure performance under simultaneous load conditions.
The Total Efficiency Ratio (TER) is calculated as the ratio between the sum of the delivered heating and cooling power and electrical power input. The TER reaches its maximum value when the heating and cooling loads are completely balanced.
As buildings become inherently more structurally energy efficient, through improved insulation and air tightness, as well as using architectural features such as solar shading, it’s important to ensure the building services are also delivering optimum efficiency. For some buildings the use of separate boilers and chiller plant is inherently wasteful, yet many specifiers prefer to continue using tried and tested hydronic systems for heating and cooling. Using multi-purpose units that optimise the performance of such systems is clearly the sensible way forward.