Simultaneously cutting out waste
One part of a building requiring heating while another requires cooling offers great potential for energy-efficiency improvements — with a little imagination. Dean Ward of Climaventa explains.
When it comes to designing energy efficient building-services systems there is now considerable emphasis on ensuring that supply of those services — be they heating, cooling, ventilation or lighting — is closely aligned to demand. It is simply wasteful to use energy to provide a service that is not needed.
A particular challenge for heating and cooling systems is that heating and cooling demands can vary considerably during the day, influenced by internal heat gains related to occupancy and changes in the orientation of the Sun. As a result, it is not uncommon for a building to demand heating in some areas and cooling in others — all at the same time.
This is nothing new, of course, and there are various ways to address this issue. Hydronic systems such as 4-pipe fan coils, for example, are a very common way of providing both heating and cooling, but typically they will use separate boiler and chiller plant. The trouble with that is that running boilers and chillers at the same time is potentially wasteful of energy. The boiler plant uses fuel to generate heat for one part of the building while the chiller plant uses energy to extract heat from other spaces and reject that heat to the outside air.
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| Climaveneta chillers that can simultaneously provide heating and cooling are available with cooling capacities from 36 to over 900 kW and can achieve energy savings of around 40% compared with a combination of boiler and chiller. |
Clearly the ideal solution from an engineering perspective is to use an hydronic system that can deliver simultaneous heating and cooling to different spaces — as and when they need it and without wasting energy. Such an ‘all-in-one’ system should also be capable of using the heat produced by generating chilled water for heating — and vice versa.
Suitable systems are now available on the market. Field tests and live installations have shown they can reduce primary energy consumption by 40% compared to separate boiler and chiller plant.
The main difference with such units, compared to traditional reverse-cycle heat pumps, is having two refrigerant circuits that can operate independently of each other. Thus the hot water is produced in a different heat exchanger to the one used to produce chilled water, thereby maintaining separation of hot and cold systems.
When only chilled water is required, the unit operates like a simple chiller, rejecting heat to the atmosphere through an air-to-refrigerant condensing coil.
In heating-only mode, the unit operates as a heat pump, extracting heat from an external source and channelling it through the evaporator to heat water for the building. The external heat source can be air, groundwater or geothermal.
Where hot and chilled water are required simultaneously, the unit behaves like a water-to-water unit, managing condensation and evaporation on two separate heat exchangers connected to the two circuits. The cooling and heating energy are provided, respectively, to evaporator and condenser, via heat exchangers that are hydraulically coupled to the cooling and heating circuits.
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| Three Polivalenti chillers that can simultaneously provide cooling and heating comprise a miniature district heating and cooling system at La Forgiatura shopping centre in Milan using water from the water table as a heat-exchange fluid. |
At La Forgiatura shopping centre in Milan, for example, three Climaveneta Integra multi-purpose units have been used to create a miniature district heating and cooling system using water from the water table as a heat-exchange fluid.
As with many other items of plant, selection is typically based on peak demand, so the units operate at part-load for most of the year. It therefore makes sense to specify inverter control of the compressors in these units to optimise operating efficiency at part loads.
Inclusion of suitable thermal storage tanks, both on the cold and hot sides, offers effective system operating modularity and optimises running costs.
There are also additional cost-of-ownership benefits. These include reduced installation requirements, as there is only one unit to connect and commission, thus minimising onsite work. Also, such units occupy less plant-room space compared to separate boiler and chiller plant.
As noted at the beginning of this article, preventing wasted energy is a pre-requisite of achieving energy efficiency. An all-in-one system that eliminates the waste inherent in traditional systems and helps to reduce carbon emissions while delivering a high level of flexibility is clearly a significant step in the right direction.
Dean Ward is applied products manager with Climaveneta UK.
