The original sandstone walls

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Assumption Set

Our current 1940's office building in the city centre is structurally sound and has been built with the original sandstone walls. The building has a North - South orientation and is 8 storeys in height.

The wall thermal insulation is poor offering a U value of 1.2Q/m2K.

The single glazing is giving a poor U value of 5.5Wm2K.

The net internal: gross external ratio is 80% and the net usable: net internal ratio is 75% which gives the building a high area of usable floor space.

The floor layout is currently offering open plan with cellular space to suit the needs of the organisation.

Storey height is 4.0m floor to floor with the current finishes having a suspended ceiling on a raised computer floor with downstanding light fittings.

The conventional oil fired boiler providing the wet heating system is currently operating at 65% and is coming closer to the end of its useful life. The thermostats on each floor in the corridor control the temperature in the rooms with no independent means of control.

The steel panel convectors are located around the perimeter of the building below cill height.

With the busy streets outside the building suffers from noise impacting on the internal environment. We have tested the air quality within the building and when the windows are open to provide ventilation we have recorded poor levels of air quality within the building.

Air tightness of the single glazed windows is poor.

The lighting is fluorescent fittings and traditional switches.

We have done an audit of the building from the carbon trust and it has confirmed that our heating and lighting costs are high compared to similar sized buildings with greater control of services and improved thermal insulation. The audit has confirmed that the high levels of absenteeism are being caused through to the building having characteristic of sick building syndrome. We have had a BREEAM assessment which gives the building a rating of poor.

The appraisal of our options is based on being in the building for a further 15 years and the forecast residual value.


The aim of this report is to discuss how our 1940's building can have its internal conditions improved to be more energy efficient and how its compares to more modern buildings.

The outcome of the report will reflect the difference from post upgrade to refurbishment and comparison with a more modern building taking into account and embracing sustainable practices and the capital allowance tax available for investing in sustainable technology.

Analysis of Existing Performance

The buildings north south orientation is unresponsive to temperature swings and with being naturally ventilated it is difficult to control the glare and noise and air pollution. The glare means greater use of internal blinds and raises the need for artificial lighting.

Solar heat gain is generally unaffected as the carpets and suspended ceiling will prevent the absorption of the unwanted heat. The poor wall construction and the poor air tightness of the windows are enabling the release of unwanted heat.

The benefits from the use of natural ventilation are being eradicated by staff leaving windows open during the night and whilst the heating is being provided. The single thermostats are aggravating this and are causing significant energy wastage.

The current boiler is running at 65% efficiency and is wasteful compared to newer models with the single thermostats failing to take into account the varying demands for heating throughout the building. The south facing offices require less heating than the north which isn't being considered with the current controls.

The existing lighting is being left on when the building is un-occupied and with the solar glare the use of natural light is not being utilised although this is a seasonal problem.

Sustainability and Corporate Social Responsibility (CSR)

The buildings current condition is failing to exhibit sustainable characteristics in terms of energy efficiency and providing a health environment for the occupants. It is advised to show that the company takes its CSR seriously that a substantial contribution is required to be invested in upgrading and re-lifting the building enabling us to stay put in the building which is important for historical reasons.

To combat the noise and air pollution against the comfort conditions and health and the heat loss natural ventilation is no longer a viable option appropriate for the building. The energy wastage is being caused through the incompatibility of the building services to the building and lack of control in there use. If the building is not updated it is anticipated the current high levels of absenteeism will certainly continue.

Building Management Systems (BMS)

With the city centre location the air and noise pollution requires a high level of intelligence in the design of the fabric and the building services.

Due to the building planning constraints we can not provide any solar shading.

Natural ventilation looks like it will have to be sacrificed for an air conditioning system.

With the central location of the controls for the heating and lighting better control is required to reduce energy costs.

There is a need for the introduction of artificial intelligence within the building with heating and lighting sensors that will respond to the buildings occupants and its usage.

Building Energy Management Systems (BEMS)

Providing further intelligence in the means of a BEMS system will hand the control for managing the energy usage over to the building occupiers which shall be controlled from a centralised point within the building. As this is the only property the company have an outstation is not practical.

The financial appraisal of the decision to invest in a BEMS will be determined by the likely payback period and the size of the building and its function.

A further factor in deciding to invest in a BEMS will be the level of sophistication in the servicing of the building in the air conditioning. Sustainability will need to be considered in making a decision.


The eventual choice of options will be drawn up based on the following criteria:

Cost - to represent value for money in the 15 years residual value.

Sustainable - energy efficiency reducing the carbon footprint of the building.

Comfort - to provide a healthy environment to work in.

Payback - The payback of the period not exceeding three and a half years.

Planning - What will the planning regulations allow us to do?

Conclusions and Recommendations

The appropriate strategy to improve the energy efficiency will be a mixture of a systematic and ad hoc approach.

Comparison with Modern Building Incorporating Conclusions and Recommendations

The current single glazed windows offering a poor u value of 5.5Wm2K is recommended to be replaced with more modern aluminium window system which will give the building an improved value of 0.4Wm2K and would be similar to that used in new modern buildings. In terms of the glare and unwanted heat gain coming through the windows we would have the windows glazed with low emissivity glass to reduce this problem and would offer better use of the space.

Mixed mode ventilation with a change over design would be achieved by placing a sensor on the windows and outdoor temperature sensor and will be based on a seasonal basis. It is thought that during the summer months we will use night cooling which will be more efficient. The amount of mechanical ventilation has the space to be accommodated within the suspended ceiling void. There is many different types of mixed mode ventilation this is one of the ways in which the desired effect could also be determined in a modern building.

The BMS will incorporate the energy management which will be controlled at the central location within the building and will give 5 air changes per hour. The BEMS incorporating the window and outdoor temperature sensors will control the motors supplying the ventilated air. In a modern building or buildings the controls would also be in a centre location or in a remote outstation. The amount of sensors in a more modern building will be designed to create the ultimate comfort conditions and energy usage which we are trying to achieve by upgrading our older building.

The conventional oil boiler will be replaced by a gas fired condensing boiler which will offer a greater 80% efficiency and reducing co2 emissions there will be the opportunity to reduce this cost under the governments capital tax allowance scheme. It will be important that we get the new boiler designed so that it will work at its most efficient. The gas condensing boilers are being used in modern buildings and will be designed similar to ensure they are working at there most efficient.

The use of the equipment within the building computers, printers, lighting, number of occupants etc will have to be factored in to the control settings for the heating and ventilation. The BEMS can control the requirements for these based on the sensors throughout the building and its occupancy. When our building was built this would not have been taken cognise of and will be factored in to new modern designs.

The existing fluorescent lighting will be replaced throughout which will be designed with the amount of lux required in each room with dimming controls available to cope with the seasonal weather and occupation of the building which will be controlled by the BEMS. There will be PIR's fitted in all areas and rooms which will help with controlling the amount of energy usage through lights being left on. The proposed lighting system is used in modern buildings and is found to have great energy saving potential when used properly.

The use of water in the toilets and kitchen areas will be controlled by stand alone presense sensors and pumps which will be controlled by the BEMS to try and conserve energy and meet the occupant's demands. The sensors are now common in buildings in trying to limit the amount of water we use.

It is proposed to introduce meters and sub-meters on each floor for all services to determine where the maximum usages are taking place.

Where our building will be different from its more modern counterparts is in the wall condition which is currently got a U value of 1.2Q/m2K. Attaching external wall insulation to improve this is not possible due to the planning constraints. Cavity wall insulation will not be effective due to the height of the building. The more modern buildings will have wall insulation batts built in or be blown in during there construction. And the external wall insulation can be fitted in the form of a render during the build.

Re-pointing of the existing walls where they are particularly weather damage will help reduce the amount of damp and improve the thermal insulation of our wall and will help to maintain the building for a greater period.

Our building compared with our more modern counterparts has a greater floor to floor height which gives us the option of running the services through the spaces in the floor and through the void above the suspended ceiling. The more modern buildings are designed with just enough void space to accommodate the services and as such do not offer any means for improvement to bigger size.

More modern office buildings are being built with insulated cladding panels in the roof which are giving greater U values through the roof. It is proposed that in our slate roof we have any damage repaired and insert loft insulation to give the building a much better U value in the roof. There are grants available for improving the U value.

To combat the amount of staff objections to the proposals we will launch an energy awareness campaign to explain the reasons why we are taking the control away from the staff. We will undertake surveys which will be used to get the optimum conditions through taking an average of what the staff would like. It is thought that the improvements will combat against the current levels of absenteeism.

The improvements will show that our company is take its corporate social responsibility (CSR) seriously and is doing its part to reduce its carbon emissions. To undertake the improvements will need a substantial capital outlay and will have a disruption on the business while the works are carried out. The capital outlay that is anticipated will be recovered through cost savings and will be paid back within three and a half years. There are grants available through the governments capital tax scheme.

The main difference within our older building if we carry out these upgrades will be that the external wall U value will still be high which will require a greater degree of heating during the seasonal periods. It is proposed that we stay in our existing building which will help to keep the companies historical background and maintain our corporate social responsibility image. The methods will also help to ensure that we can stay in the building for at least the next 15 years and will ensure that the building stay in a health environment for many years after.


To improve the internal conditions within the building it is proposed that we:

  • Replace the windows with new double glazed aluminium with low emissivity glass.
  • Introduce mixed mode change over ventilation with sensors on the windows and outside.
  • Introduce sensors in the building and take the control for the heating and the lights to a central location within the building.
  • Replace the lighting with more energy efficient lights with the right number and introduce PIRs in all rooms.
  • Replace the existing boiler with a new gas condensing boiler which has been designed to meet the buildings needs.
  • Introduce presence sensors on the pumps and taps in the kitchens and toilets.
  • Meter and sub-meter all of the services coming in to the building and at each floor.
  • Re-point the external wall to protect against dampness.

It is believed that adaptation of these improvements will satisfy the requirements that were set out in the criteria. The costs have taken into account a life cycle costing based on the building being around for 40 years. The amount of design work and further surveys required will take a period of three months. After which time a period will be required for tendering which has been allowed at present to be two months. To complete the work with a minimum amount of disruption has been programmed to take a period of 6 months.

I await your further instructions.

Main sources of reference.

  • The Facilities Manager's Energy Primer