Trial / Demo
RISE helped to design a hospital HVAC system in Italy, using the IESVE to carry out dynamic simulation modelling.
The scope of work
This energy analysis was done during the preliminary design of a hospital, which is located in the south of Italy. The primary goal was to compare different cooling solutions, focusing on comparing a water-to-water chiller, where the condenser is cooled through a cooling tower, with an air-cooled chiller.
The key parameters analysed the economic implications, the impact on water consumption and the potential energy savings.
Designing the HVAC system
In a hospital environment, air quality is crucial to prevent cross-contamination between diverse spaces. External air exclusively is introduced, maintaining six air changes per hour (ACH) for most areas, 15 ACH for the morgue and 25 ACH for the surgery area.
The supply of air, to maintain relative humidity between 45% and 55% at a temperature of 25°C (77°F) in summer, must be cooled to 13°C (55.4°F) for dehumidification. To achieve comfort, post heating is then employed, and this heat is efficiently recovered using a heat recovery chiller, contributing to the overall energy efficiency of the building, as seen below:
Energy modelling
The system that was designed is a dedicated outdoor air system (DOAS) with local post heating for all areas except the inpatient room, which has zone post heating and radiant panels on the ceiling.
Airside
For the HVAC element, the controls have been modelled in a very precise way, to guarantee a perfect control of the relative humidity and the internal temperature:
Here is an example report of how the temperature of the air supply is controlled:
Chilled water loop
Two different solutions were designed: one with water-cooled chillers, and the other with air-cooled chillers, both modelled in a very detailed way. Both solutions have a heat recovery chiller which is air-cooled, and has been designed based on the maximum requirement for heating and cooling of the building. It can work in cooling-only mode if needed, and there is also a reversible heat pump for backup.
Hot water loop
The hot water loop has been created to precisely reflect the system’s design, with the correct division of secondary pumps to address the pump’s energy consumption.
Results
The following graph shows the total energy consumption of the building during the summer (air-cooled is in red and water-cooled is in blue):
The water-cooled solution is more energy efficient, yet more expensive by €380,000. However, it lowers the energy consumption by 460,000kW. Since energy in Italy is expensive - 0.25 €/kWh - in four years’ time, the investment will be repaid.
The more interesting aspect is that, thanks to the output available in IESVE, the amount of water used by the cooling tower has been calculated, and it is almost 10000 m^3 of water. This resource will never be sufficient in the south of Italy, in particular over the next years because of the climate change, so the air-cooled solution was chosen.
The graph below shows the energy consumption of various elements, with fan energy consumption having the most impact.
The next phase of the project will use more efficient air handling unit (AHU) fans.
This graph highlights electricity consumption:
