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HVAC SYSTEMS


6,000 5,000 4,000 3,000 2,000 1,000 0


Hours (1 year) Figure 5: Hourly cooling load for the building.


2,500 2,000 1,500 1,000 500 0


Hours (1 year) Figure 6: Hourly heat rejection transferred for heating. lighting power density multiplied by the


lighting schedules and the usage factor). Exterior lighting: This is the exterior


Heating: All thermal (steam) or electrical heating used in the building (thermal losses of the envelope and heating of outdoor air


for ventilation). Humidification: This is the


humidification that is essentially required


because of the outside air ventilation. Cooling: This is the compilation of the consumption of the cooling equipment used in the building (chillers, refrigeration


equipments, etc). Heat rejection: This includes the cooling


38


Services: This includes all the building thermal usages (essentially all usage of steam for thermal heat processes in the kitchen and sterilisation unit, including the distribution losses).


lighting (not used for this simulation). Equipment: This includes all the electric equipment used in the building (imaging equipment, electronic equipment, escalators, etc).


tower energy usage and the condenser pumps. Pumps: This includes the energy of the


pumps for the heating loops and the chilled water loops (all pumps related to cooling and heating).


modern hospital). DHW: This is the energy (steam or


electricity) used for the heating of the domestic hot water (hot water used for hydrotherapy, dishwashers, baths, etc).


The analysis of this chart shows how important the heating requirements are (including the humidification). It represents more than 42% of the total energy usage of the reference (non-efficient) building. It is clear that something should be done to lower the energy usage for heating. Figure 2 shows the thermal requirements


associated to the outside air heating, the outside air humidification, and the heating of the building envelope. The total energy for


Air handling fans: This is the energy used


by the fans needed for the air handling systems (this is a major user of electricity in a


Heat transfered from a 350 tons chiller


Hourly cooling load


these items is 29,300,000 kWh (equivalent). Figure 3 shows the thermal


requirements associated to the heating of the components of the building envelope (walls, roof, and windows). The total energy for these items is 6,560,000 kWh (equivalent).


Improvement for better energy efficiency Improving the roof insulation has an impact on 0.42 x 0.224 x 0.091 = 0.85% (less than 1%) of the building’s total energy consumption. In comparison, heat and humidity recovery on the exhausted air to preheat and humidify the incoming fresh outside air for ventilation will have an impact on 0.42 x 0.776 = 32.6% of the building’s total energy consumption. Heat recovery of exhausted air by an enthalpy and sensible heat recovery device (such as an enthalpy heat recovery wheel) offers a way to drastically reduce the amount of energy required for heating. With an appropriate heat recovery design, the building’s total energy consumption could be reduced by 25%. Figure 4 shows the hourly heating load for heating the building after the implementation of the heat and humidity recovery on exhausted air. The remaining sensible heating requirement (without humidification) is 6,000,000 kWh. Another way to improve


energy efficiency is by the use of air-conditioning chillers in a heat pump mode to recycle inside heat gains for fresh air or perimeter heating. The inside heat gains are generated by imaging systems,


sterilisation, cooking equipment, and all electrical equipment in use in the building. Important thermal loads in a hospital are generated and, in most cases, it is a result of the intensive use of steam. If the heat generated by these steam processes could be recovered by air conditioning systems, it


‘The analysis of the distribution of energy shows that almost 50% of the energy usage is related to special thermal (37.2%) or electrical (11.4%) equipment specifically used in hospitals.’


IFHE DIGEST 2014


Hourly heat rejection transferred for heating (kW)


1


285 569 853 1137 1421 1705 1989 2273 2557 2841 3125 3409 3693 3977 4261 4545 4829 5113 5397 5681 5965 6249 6533 6817 7101 7385 7669 7953 8237 8521


1


286 571 856 1141 1426 1711


1996 2281 2566 2851 3136 3421 3706 3991 4276 4561 4846 5131 5416 5701 5986 6271 6556 6841 7126 7411 7696 7981 8266 8551


Hourly cooling load (kW)


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