The Building Model

The main services are carried out using the building model as a base. Once the base model has been created within the software, the room/zone templates are created. Each room/zone type has an individual template which allows activities, temperatures, HVAC systems, lighting, occupancy, internal gains, ventilation to be set for each. Profile's can be created for various aspects depending upon the level of simulation required. The typical profile used is a time schedule for plant operation and occupancy times etc. Profiles also enable     other actions to be performed based on set criteria - for instance windows can be opened based on internal temperature levels or carbon dioxide levels - complex AND/OR logic functions can be set to enable greater representation of the actual building. Templates are then assigned to rooms. Next construction elements are entered into the database for both solid and glazed surfaces, and then assigned to the models surfaces. The buildings orientation is then set and its geographic location assigned to the nearest data set. After this very simplified overview of the set up procedure, the building is now ready to start running simulations.

The amount of data entered is dependant upon the level of simulation being carried out. For instance the Part L calculations use the governments standard templates based on the room activity setting, rather than setting up new templates.

To simplify the physical input of the building geometry into the software, the most common approach is to overlay DXF files and then trace around the rooms. This provides the main floor plans; however windows and roofs will still need to be manually added.

Greater integration is possible from popular CAD software. For instance ARCHICAD provides a high level of integration and allows the complete building form, window arrangement, roofs, construction data to be transfered from the architects drawing directly into the modelling software. This is a significant step towards full Building Information Modelling (BIM). From experience this requires some discipline from the architects in the correct trimming of the zones and then the re-trimming when changes are made; however significant time and resources can be saved by not having to repeat the building set up.

Skip to top

Dynamic Thermal Simulation

Dynamic thermal simulation (DTS) allows the buildings thermal performance to be evaluated over a period of time based on changing external and internal conditions and activities. DTS is a holistic view of the building using real climatic data for the buildings location. It allows changing internal occupation levels and provides the facility to simulate users interaction with the building (for instance opening windows when hot etc). 

Once the building and templates have been set correctly, the simulation can be run. A vast amount of data is generated by the software and the variables analysised will depend upon the objective.

For instance, the heating load can be assessed throughout the year. This will show that the peak static load typically calculated will only occur on a few occasions. Using the dynamic output (Fig 1.1), a more realistic base load can be reviewed and used for the sizing of heating equipment. This enables a reduction in capital cost as well as the more efficient integration of low grade heat sources. Low grade heat sources can include renewable technologies such as biomass boiler, heat pumps, solar panels and so on.

Internal temperatures can be simulated and areas of overheating can be highlighted. For assessing a naturally ventilated building this is becoming increasingly important as it enable problem rooms to be reviewed during the design stage and measures taken. Further simulation can look at improving the buildings performance by possibly modifying the thermal structure, improving ventilation or solar shading. If DTS is implemented during the early stages of the design it can be used to review room locations - the relocation of rooms could avoid areas of overheating by moving non-critical activities to "warmer" regions.

DTS is a very powerful tool for optimising a buildings thermal performance. The range of options and scenarios which can be simulated is vast. The earlier in the project DTS is employed, the greater the benefits to the design team. 

Skip to top

Bulk Air flow Simulation

Bulk air flow simulation builds on the dynamic thermal simulation by adding dynamic air flow patterns. This allows a more accurate representation of natural ventilation to the building. 

There are three main ventilation groups to a building (1) natural infiltration due to the air tightness of the build, (2) mechanical ventilation due to HVAC plant etc, and (3) natural ventilation due to opening windows etc. 

Air infiltration is usually input into the model based on a simple air change rate. Typical infiltration figures are provided by the Chartered Institute of Building Services Engineers (CIBSE) based on application; however due to the use of air pressure testing, infiltration rate can be taken as 1/20th of the air permeability result (or design target). Therefore an air test target of 10m3/hr.m2 @ 50Pa equates to an infiltration rate of 0.5 ACH/hr.

Mechanical ventilation is added to the model either via an air change rate, air flow per meter square, or even a fixed air flow amount, to name a few methods. Profiles are applied to the operation of the equipment to simulate the plant operation times. More complex profiles can be applied to simulate trickle/boost modes, or even based on variables such as temperature, CO2 and so on.

Natural ventilation can be added on a basic level as a set air flow or air change rate. For instance you may conclude that opening a window will provide 4 air changes per hour to the room. This can then be simulated by the model in a similar way to mechanical ventilation.

The bulk air flow module allows a far greater level of dynamic simulation of natural air flow. It simulates air flow through the building, i.e. between rooms, due to natural effects. This may be due to opening and shutting windows or purpose ventilation opening, or simply the leakage around a window or door. The amount of air into and out of the building is based upon the wind speed, building orientation and ventilation paths. This air flow has an impact both in heating and cooling operations; however the main benefit of this calculation is to review natural ventilation strategy in relation to building overheating. For instance, during summer periods, the peak internal temperatures can be simulated based upon the window openings. Each window type will need to be set up as a template with the percentage of opening area available. A seperate calculation needs to be carried out on the windows to determine the opening area. These window types (or more general opening types as they do not need to be windows) are then applied to the openings on the building model. The simulation can then be run to calculate the air flows into and out of the room or zone. This dynamic ventilation air flow is then used in the calculation of the other properties within the room. Usually the peak temperature or "how many hours does the temperature exceed 28 deg C" are the main considerations, however other factors such as CO2 levels, the amount of fresh air introduced to a space, humidity levels, can all be reviewed.

Again by applying profiles to the windows (or openings) then other scenarios can be simulated - nighttime ventilation, build up of heat within an office/school over a weekend, build up of heat during a home during the day before the occupants return in the evening and open the windows, and so on.

In this manner, the bulk air flow simulation can also be used to determine the background ventilation to the building in accordance with Part F of the Building Regulations. The previous method of applying a ratio of windows-to-floor area in not applicable and more dynamic approachs are often requested by Building Control. By reviewing natural infiltration and leakage around openings then a background level of ventilation can be calculated.

Skip to top

CFD - Computational Fluid Dynamics

Computational fluid dynamics (CFD) is a step on from the dynamic thermal simulation and bulk air flow analysis.  The CFD calculation uses the thermal loads generated via the dynamic thermal simulation and provides a more detailed analysis of the air flow characteristics and temperature distribution within a specific zone. 

It allows a far greater level of detail as to the air distribution and temperature stratification within a zone. Where as the DTM and bulk air flow allow the temperature within a zone to be simulated, the CFD allows the temperatures at different points within that zone to be analysised. For instance the head-to-floor temperature difference can be reviewed. Complex spaces such as atrium can be reviewed to show temperature limits within the occupied zone, rather than an simple single zone temperature calculation.

For naturally ventilated buildings, CFD provides a valuable tool in predicting temperatures and air flows within the occupied zones. For mechanically ventilated buildings, CFD can improve the efficiency of air terminal locations to minimise stagnant areas, reduce cross-ventilation, improve air performance within the zone. 

The CFD simulation builds on the information already entered for the building model and the templates etc set up in the DTM. The boundary conditions for the zone can be input from the DTM, selecting a specific time and conditions for the simulation. Additional information can be entered in relation to objects within the zone - to simulate people, furniture etc - to enable a more accurate prediction of the air flows.

Skip to top

Daylight Analysis

Lighting levels within a room are very much an individuals perception. However a room is typically considered daylight if it has an average daylight factor of over 2%. A room of less than 2% will  be perceived as "gloomy". A room above 5% will be perceived as "well daylit".

With the building model set up correctly and the window openings in the correct position, the levels of natural daylight can be simulated.  The external illuminance level can be set at a specified amount, although typically this is based upon the standard "CIE Overcast Day" level.

Other variables are - surface finishes, working plane height, lighting grid size, borrowed lighting and so on. Outputs are provided in tabular form showing minimum, maximum and average daylight factors and lux levels. Outputs are also available in graphical form showing the lux of daylight factor contours. 

Skip to top

Solar Shading Analysis

Based on the buildings external geometry, orientation and location, the impact of the solar path can be simulated. Simulations can be run for different periods (times, months etc) to show which surfaces are exposed to sunlight and which areas are shaded. Outputs can be graphical in still images or even short AVI streams, or in tabular form. 

Local shading and adjacent buildings (or objects) can be added to the building model and simulated to analysis the effect on the building in terms of the direct solar levels. 

The use of shading in terms of roof overhangs, window details, or brise-soleil can be modelled. Rather than using a manufacturers set shading coefficient, the brise-soleil is physically modelled to scale and located on the building to show its real impact. The materials used for the shading device can be adjusted to suit different models.

Other shading devices such as integral blinds can be applied to the windows and provided with a template to control its operation - for instance the blind can be closed when the direct solar levels exceed a set point.

Solar shading, whether external or internal, helps to reduce solar heat gain to a space as well as reduce direct solar, or glare. However too much solar shading will have a negative impact on the amount of natural daylight available to the space, therefore a careful balance needs to be maintained - otherwise the savings in the cooling energy reduction will be offset by the additional artificial lighting energy required. 

Skip to top

Part L and Part F Building Regulations Compliance

During the early stages of a buildings design, it is important to be aware of how decisions taken will affect the buildings compliance with both Part L (Energy) and Part F (ventilation) of the Building Regulations.

Since 2006, compliance with Part L has been a holistic approach to the whole buildings design in relation to its thermal performance and building services installed, rather than the previous route of simply achieving certain constructional U-value targets. With the proposed improvements to the regulations due in 2010, achieving compliance will require a greater understanding of the building thermal performance. 

Part F can be reviewed using the bulk air flow simulation as described in the section above. Part L is reviewed and can lead on to the production of Energy Performance Certificates - see section below.

Independent advice can be provided on the building at any stage during the design or construction, however it is recommended that both Part L and Part F are considered early on to avoid any potential issues.

Skip to top

Energy Performance Certificates

non-domestic

Energy Performance Certificates (EPC's) are required for any non-domestic building when it is sold, rented out and constructed. Please follow thislinkto the governments web site.

We are able to provide energy performance certificates for any non-domestic building within the UK. We have engineers accredited for Level 3, Level 4 and Level 5 using thermal simulation. Our engineers are accredited through CIBSE Low Carbon Energy Assessors - one of the Uk's leading and most reputable accreditation agency. 

In accordance with government guidelines, we do not use data collectors; each assessor will carry out a survey of the building. Fully dimensioned building plans will be required - we can organise this using third party providers if none are currently available (for very small property we can include to carry out our own building measure). The greater the level of detail provided and/or obtained from site, then the more accurate and representative the EPC result.

domestic

Domestic EPC's are required for homes being sold, rented, constructed or refurbished. Please follow thislinkto the governments web site.

We are able to provide energy performance certificates for new-build or refurbished properties only. Our engineers are accredited through STROMA. As the properties are either being constructed or refurbished, then building plans are usually available from the architect or surveyor. The production of domestic EPC's will require the engineer to visit the property to ensure that the details used in the calculation are in accordance with the "as-built" condition.

Skip to top