Building simulation plus...
Being able to include detailed performance data for equipment into simulation-based design calculation brings new capabilities to building simulation — a feat that has been achieved by EDSL and Mitsubishi Electric, as Ken Sharpe explains.
Building simulation software is a powerful tool for predicting such things as heating, cooling and lighting loads of a building as frequently as every hour. It can take account of solar shading and weather data. One of its key outputs is an annual energy requirement for a building, which can be used to compare the performance of a design with a notional building according to Building Regulations. It can also be used to compare a number of designs.
Quite a different question is how much energy will be used by the actual boilers, air-conditioning systems and lighting in a building. Factors affecting the outcome will, of course, be the performance of equipment at full load and part load. Performance figures based on periods of operation at full load and various part loads can help compare equipment — but how will equipment perform in an actual building?
That is a question that has been addressed by EDSL, which develops thermal simulation software, and air-conditioning manufacturer Mitsubishi Electric.
EDSL’s Tas (thermal analysis simulation) software is widely respected for its accurate analysis and predictions of the thermal properties of a building’s design and its ability to predict ongoing energy consumption based on real and localised weather data throughout a year.
Now, the two companies have collaborated to bring detailed performance data of Mitsubishi equipment into Tas. What that brings to the party is to enable building designers to include actual part-load performance data and control logic for Mitsubishi Electric equipment.
According to Alan Jones, managing director of EDSL, this is the first time that detailed equipment performance data has been automatically included into simulation-based design calculations. He explains, ‘This is important because it allows all of the energy-saving innovations that Mitsubishi Electric has designed into its equipment to be taken into account during a detailed hourly simulation of building, plant and controls to calculate annual energy use, CO2 emissions and occupant comfort.’
Another benefit is that the end results will be sufficiently accurate and robust to adhere to building energy labelling requirements.
The accuracy of the approach was assessed by carrying out a simulation for a 2-storey office building in Chelmsford for which Mitsubishi had a year’s energy-consumption data. There were five City Multi 2 VRF heat-recovery systems comprising 25 indoor units. Ventilation requirements are met by a Lossnay heat-recovery unit on each floor.
The long facades of this building face east and west and have a large amount of glazing, so the system is designed to utilise heat recovery to use heat extracted from areas requiring cooling to heat other areas. There will be periods of the year when heating and cooling are required, and also periods when only heating or cooling is needed.
Since the only weather data available from the study was the daily peak dry-bulb temperature, the Swindon test reference year was selected as a reasonable fit.
EDSL has prepared detailed graphs of simulated and measured energy consumption for each week of the year for which data was gathered and comments that the simulated model shows good qualitative agreement with the measured data. The measured energy consumption for the whole year was about 10% higher than the simulated result for the installed equipment.
The next stage was to put the simulation software to work by assessing the effectiveness of updating the installed system to units from the latest catalogue (2011). Comparing the two simulations showed a 34.6% reduction in annual energy consumption — a remarkable improvement in such a short period of time.
Another trick carried out by EDSL was to update the entire building model to match the 2010 notional-building requirements, including the geometry. The model was then taken through the UK Building Regulations 2010 Studio, and all inputs for the actual building set to the notional defaults. It is then possible to make a direct comparison of a notional system and a VRF system.
In Part L, a VRF system is compared against a fan-coil system with a chiller for cooling and a heat pump for heating.
The notional chiller has an EER of 4.5 and a distribution efficiency of 80% — giving an overall chiller EER of 3.6. The notional electric heat pump has a COP of 2.7 and a distribution efficiency of 90% — giving an overall COP of 2.43.
A new systems model was created and linked to the building simulation results file from that Part L simulation. This systems file contains the detailed VRF system with the imported Mitsubishi City Multi R2 equipment. This model is simulated for an entire year, and the seasonal efficiency for heating and cooling calculated.
The seasonal heating COP for the VRF system was 3.74, indicating 35% less energy use compared with the notional electric heat pump.
The seasonal cooling EER for the VRF system was 4.67, indicating 23% less energy use.
The EPC rating of the notional building with chiller and heat pump was B(34), which is improved by the VRF system to B(31).
Commenting on the project, Alan Jones of EDSL says, ‘Mitsubishi Electric was completely transparent with the performance data given to us to include in the Tas program, which was an essential requirement in providing the accurate modelling and simulation results that our customers have come to rely on.’
Martin Fahey, Mitsubishi Electric’s sustainable-solutions manager, adds, ‘This software give building designers the tool to accurately demonstrate the energy levels that individual equipment will have on a building. This then allows installers and end users to clearly see the relative performance impact that one product or configuration can have over another.’