MODELLING HVAC PREDICTED VS ACTUAL USE
The total annual consumption and
cost for the measured, validation model with installed equipment, and the 2011 equipment model, are detailed in the table on page 65. The simulation shows that the new models are 34.6% more efficient than currently installed models for this building.
The actual measured performance and costs of the systems closely follow the simulation
65. From the table we can see that the blue system needed to supply both heating and cooling for 959 hours, whereas the red system only had 43 hours. This information could be used to optimise heat recovery in the design.
First floor, sensible load – Day 50, hour 7 First floor, sensible load – Day 50 hour 12
Conclusion The simulated model shows good qualitative agreement with the measured data. The model contains reasonable assumptions based on engineering judgement and utilises industry tools, such as the Swindon TRY weather file and NCM Activities database, to fill in the blanks for areas where monitoring had not been undertaken. The new manufacturer data import facility for EDSL Tas is used to provide realistic results for City Multi, Mr Slim and CAHV Mitsubishi Electric models. The building and plant simulation capture the part load characteristics and give consumption results that are close to what you would expect to find in practice.
First floor, sensible load – Day 166, hour 15
Updating equipment to units from Mitsubishi 2011 catalogue Taking the model that has been developed for the qualitative validation, it is possible to update the air conditioning units to the latest Mitsubishi Electric equipment.
Notional
City Multi R2 System Seasonal energy efficiency ratios
66 CIBSE Journal January 2013
Heat SSEEF 2.43 3.74
Cool SSEER 3.6
4.28
Simulating updated equipment against Part L notional building The entire building model is updated to match the 2010 notional building requirements, including the geometry. The model is taken through the UK Building Regulations 2010 Studio, and all the inputs for the actual building are set to equal the notional defaults. In this way, building loads will be identical, allowing a direct comparison between the notional system and variable refrigerant flow (VRF) system effectiveness. In Part L a VRF system is compared against a fancoil system with chiller for cooling and an electric heat pump for heating. The VRF system is set to equal the efficiency for the notional system. The notional chiller has a COP of 4.5 and a distribution efficiency of 80%. The notional electric heat pump has a COP of 2.7 and a distribution efficiency of 90%. This gives an overall chiller efficiency of 3.6 and an overall electric heat pump efficiency of 2.43. The Part L calculation is simulated
and the Building Regulation UK Part L (BRUKL) document shows that the actual and notional building exactly match with a target emissions rate (TER) and building emissions rate (BER) of 17.1 kg CO2
/m2
annum. The EPC rating is B(34). A new systems model is created and
linked to the actual building simulation results file from that Part L simulation. This systems file contains the detailed VRF system with the imported Mitsubishi Electric equipment. This model is simulated for the entire year and the seasonal efficiency for heating and cooling is calculated (before left). The Part L calculation is repeated, with
the new efficiency values entered for the VRF system. The BRUKL document now shows that the actual building has a BER of 16.1kgCO2
/m2 building TER remains at 17.1kgCO2 References
Mitsubishi Electric – The measured energy consumption of 5 City Multi R2, 2 Pipe Heat Recovery systems at Springfield Lyons Approach, Chelmsford over a one year period.
/
annum. The EPC rating is now B(31) an improvement of 3 points. CJ
/
.annum and the Notional /m2
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