Small School HVAC Design & Building Performance Simulation

Project Overview

This project involved the thermal modelling and HVAC design of a small educational building in Birmingham using IES Virtual Environment and ApacheHVAC.

The building consists of:

• 1. Two 60 m² classrooms

• 2. One 20 m² staff office

• 3. One 10 m² WC

  • Total conditioned floor area of 150 m²

• Total conditioned volume of 450 m³

The completed model combines mechanical ventilation, heat recovery, room-level heating and cooling, central heating and cooling plant, occupancy profiles and annual dynamic simulation.

The final HVAC arrangement uses a dedicated outdoor-air system (DOAS) with sensible heat recovery together with four-pipe fan-coil units (FCUs) serving the occupied rooms.

Cooling is supplied by a water-cooled electric chiller, while heating is provided through a central hot-water system served by two boilers.

Building Model

The thermal model was developed to represent the different operational requirements of classrooms, office accommodation and sanitary spaces.

Representative fabric properties used within the model included:

• Glazing U-value: approximately 1.57 W/m²K

• External doors: approximately 2.17 W/m²K

• Ground floor: 0.22 W/m²K

• Roof: 0.18 W/m²K

• Classroom external walls: approximately 0.50 W/m²K

• Office external walls: approximately 0.82 W/m²K

• Infiltration: approximately 0.20 air changes per hour

Internal gains included occupant sensible and latent heat, lighting and equipment loads.

Lighting was modelled at 6 W/m², while equipment gains were modelled at 5 W/m².

HVAC System

The ApacheHVAC model separates ventilation requirements from room heating and cooling.

Dedicated Outdoor-Air System

The DOAS provides conditioned outdoor air to the classrooms and staff office. The system delivers a total design outdoor-air flow of: 670 L/s

distributed as follows:

Each classroom receives approximately 10 L/s per person of outdoor air.

A separate 30 L/s extract system serves the WC.

Sensible heat recovery is incorporated into the air-handling system to reduce the heating and cooling required to condition incoming outdoor air.

Room Heating and Cooling

Independent four-pipe fan-coil units provide room-level heating and cooling.

The occupied temperature settings are:

Heating: 21°C
Cooling: 24°C

During unoccupied periods, the model uses:

Heating setback: 16°C
Cooling setback: 28°C

The building operates primarily on weekdays, with HVAC operation beginning ahead of occupancy to allow the rooms to approach their occupied temperature conditions.

Fan-coil units respond independently to the thermal requirements of each space.

Heating and Cooling Loads

Dynamic load calculations were completed for the four modelled spaces.

Classroom 01 produces the highest individual cooling demand.

The combined individual room cooling peaks total approximately 12.17 kW.

The coincident system cooling demand is slightly lower at: 12.032 kW

comprising:

• 9.168 kW sensible cooling

• 2.864 kW latent cooling

The difference reflects the fact that individual room peak loads do not occur at exactly the same time.

Coincident space-heating demand is approximately: 1.485 kW

Central Plant

The completed HVAC model includes central chilled-water and hot-water systems.

Cooling Plant

The cooling system uses a: 20.62 kW water-cooled electric chiller

with approximately: 24.11 kW condenser/tower duty

The annual simulation recorded a maximum chiller load of approximately: 11.98 kW occurring on 15 August at 15:00.

Heating Plant

The heating system consists of two boilers, each rated at approximately: 11.57 kW

giving a total hot-water plant capacity of: 23.14 kW

The annual simulation recorded a maximum boiler load of approximately: 23.02 kW on 17 February at 08:00.

The maximum recorded heating-coil demand was approximately: 21.83 kW.

Ventilation Performance

Ventilation performance was assessed using the simulated mechanical outdoor-air supply and indoor CO₂ concentrations. Mechanical daily-average CO₂ concentrations remained below 1,000 ppm in the assessed spaces.

The highest reported values were approximately:

The results demonstrate that the mechanical ventilation system provides the required outdoor-air service while maintaining good indoor air-quality conditions under the simulated occupancy.

Annual Energy Performance

The completed annual simulation produced the following whole-building results:

Modelled Energy Breakdown

Space heating represents the largest modelled energy demand, while cooling energy use is relatively small over the annual simulation.

Dynamic Room Performance

Time-series outputs were reviewed to understand how the HVAC system responds during occupied and unoccupied periods. For Classroom 01, for example, airflow increases during the morning warm-up period, remains elevated throughout the main occupied period and then reduces progressively after normal operating hours. Winter temperature outputs show the classroom recovering towards approximately 21°C following morning HVAC start-up.

Across the occupied simulation periods, the recorded room air-temperature ranges were:

The lower temperatures occur mainly around start-up periods following the unoccupied heating setback.

Thermal Comfort Assessment

Thermal comfort was reviewed using TM52, BB101 mechanical comfort criteria and ISO 7730.

TM52 Assessment

The occupied-period TM52 assessment produced a pass for all four rooms against all three TM52 criteria.

The assessment recorded:

• 0.0% exceedance for Criterion 1

• 0.0°C·h weighted exceedance for Criterion 2

• 0.0°C maximum exceedance for Criterion 3

Because the final building model is mechanically conditioned, the TM52 results are presented as supplementary thermal-comfort information rather than as evidence of a free-running naturally ventilated building.

BB101 Mechanical Comfort

The BB101 mechanical comfort assessment identified a limited number of occupied hours with predicted mean vote above +0.5:

The simulation contained approximately 1,827 mechanically conditioned occupied hours.

Indoor CO₂ performance remained within the assessed daily-average criteria.

ISO 7730

The three principal occupied rooms were also assessed using ISO 7730 thermal-comfort criteria.

Under Category C, all three assessed rooms achieved 100% of the evaluated hours within ±0.7 PMV.

Maximum predicted percentage dissatisfied values were approximately:

• Classroom 01: 12.84%

• Classroom 02: 12.95%

• Staff Office: 12.79%

The more demanding Category B assessment was not achieved throughout the complete occupied period.

Project Outcome

The completed model demonstrates the development and simulation of a multi-zone school HVAC system within IES VE ApacheHVAC. The final model incorporates:

• 1. Dynamic thermal modelling

• 2. Room-specific occupancy and internal gains

• 3. Dedicated mechanical outdoor-air supply

• 4. Sensible heat recovery

• 4. Four-pipe fan-coil units

• 5. Independent room temperature control

• 6. Central chilled-water and hot-water systems

• 7. Chiller and boiler sizing

• 8. Mechanical extract ventilation

• 9. Annual energy simulation

• 10. Indoor CO₂ assessment

• 11. TM52 thermal-comfort screening

• 12. BB101 mechanical comfort assessment

• 13. ISO 7730 comfort assessment

• 14. Hourly room and HVAC performance analysis

The ApacheHVAC network completed successfully, with all modelled rooms connected to the intended HVAC system and annual simulation results generated for room conditions, airflow, heating and cooling demand, central plant operation, energy consumption and thermal comfort.

The project provides a complete example of applying building physics, dynamic thermal simulation and detailed HVAC modelling to an educational building using IES VE.

Key Results

150 m²
Conditioned floor area

670 L/s
Design outdoor-air supply

12.03 kW
Coincident peak cooling demand

1.49 kW
Coincident space-heating demand

20.62 kW
Installed chiller capacity

23.14 kW
Hot-water plant capacity

34,050 kWh/year
Modelled annual site energy

227 kWh/m²·year
Site energy intensity

44 kgCO₂/m²·year
Modelled operational carbon intensity

<1,000 ppm
Mechanical daily-average CO₂ across assessed spaces