nakedgreenbuilders.com - Energy audit

Energy audit

Existing buildings can also be improved, and this does not necessarily require high-tech expensive solutions. It is often the easier, cheaper, less visible measures which make the most difference.

A building audit can be used to give an overview of your building's, and its occupants', environmental performance. We can identify where your attention should be prioritised.

Friday 29^th July 2005

We were are asked to provide an energy audit of an existing office building. A preliminary study was conducted to observe and collect data. The following provides a brief overview of the building’s performance, identifying some specific areas of concern, and others that require further investigation.

Building construction

Built c.1990, of heavyweight construction, the building consists of masonry cavity walls, cast concrete floors and coffered concrete ceilings, which are all high thermal mass. The 3rd floor does not have a concrete ceiling. The building is naturally ventilated and open plan, and has retrofitted air conditioning. It has good solar aspect, and is buffered to the north by an adjoining building. There is great potential to reduce the building's energy consumption.

Main findings

We looked at the thermal performance, heating and ventilation, electricity and gas consumption; including building services, lighting, appliances and equipment; and natural daylighting. We estimate that the building's energy consumption is currently using in excess of 100,000KWh per year, of which about 60% is being used for space heating. This is typical for buildings of this type.

The main areas for concern that we have identified are:

Inadequate levels of loft insulation
The intended photovoltaic array, if loft insulation is not brought up to standard first
Inappropriate use of air conditioning , especially in the server room
Ceiling tiles preventing exposure of thermal mass
Insufficient cross-ventilation
The large glazed area at the front of building with ineffective louvres
High-powered photocopier being used as a printer.

Thermal performance & heating

Loft insulation

The roof is constructed with corrugated galvanised steel and insulated and covered with rubber membrane. Measurements suggest that there is 70 mm between the highest point of the ceiling and the exterior of the roof. Of this, 20 mm is probably board to protect the membrane, so there could be as little as 50 mm of insulation, probably of a rigid, closed-cell type. 50 mm of polyurethane foam would have a U-value of 0.46 W/m2K. This is a very insufficient level of roof insulation, and would not comply with current building regulations.

Heating accounts for 60% of the building's energy load, and it is likely that most of this is lost through the roof, so insulating well would make a significant reduction in energy use. This is the area where greatest savings could be made. The lack of good insulation is probably also partially contributing to the building’s overheating problem.

Additional insulation must be installed before the winter. This will be easy to do now, but nearly impossible when photovoltaics (PVs) are installed. Therefore if PVs are installed before insulating, more energy will be lost through the roof than the PVs will ever hope to generate. The payback time of insulating compared to that of installing PVs could be calculated as part of further investigation.

Our recommendations to the client:
- Install a further 200 mm of polyurethane rigid foam fitted to the outside of the roof, covered with an EDPM membrane, before the PVs are installed. We would be happy to provide this service.
- Could supplement this with a green roof to provide thermal mass to buffer external temperatures, protect the roof and increase the output of the solar panels from the cooling effect of evapotranspiration.
- Allow further investigation of the insulation levels in the sides of the roof and walls, to see if they can also be improved.

Thermal mass and cross-ventilation

High mass buildings can help to buffer diurnal temperature changes by absorbing heat and releasing it when room temperatures have cooled (e.g. at night), if the mass is exposed. This can reduce heating and cooling requirements. However, the ceiling, where heat gathers, has been almost entirely covered by ceiling tiles which prevent heat being absorbed. The 3rd floor, which suffers from the worst overheating, has no thermal mass in the ceiling.

Cross-ventilation is required to cool the thermal mass. There is inadequate cross-ventilation in the building because windows are on perpendicular walls and there are closed stairwells, but improvements could be carried out as part of further work. If the building were allowed to cool down overnight, air conditioning may never need to be used.

Our recommendations to the client:
    - remove ceiling tiles on the ground, first and second floors
    - fit window latches so that windows could remain open at night but still be locked
    - have electromagnetic door release mechanisms which are linked to the fire alarms, so that doors can be left open.

Air conditioning

Although the use of air conditioning is denied, it seems to be used regularly during the summer. Air conditioning is energy intensive, especially when misused. Windows should be closed when air conditioning is on, to contain the cooler air, but it was observed that windows were open at the same time. On the 3rd floor, this could be partly because the photocopier is making the people sitting near the air conditioning unit uncomfortably hot. They then turn on the air conditioning, but people on the other side of the room need only to open a window to cool down.

In the basement, the servers are assisting in the overheating of the building as they’re in a small room with no ventilation. Temperatures in excess of 33C were recorded. Air conditioning is being installed for the servers, despite the fact that there is a window and door which could be opened in the server room! The air conditioning unit will be working extremely hard to counteract these temperatures, which will be energy intensive. In the winter, the extra heat could be used to heat the building .

Our recommendations to the client:
- open the doors and windows
- modify the door and windows if security is required.

Louvres

The large glazed area on the ground floor is gaining too much heat in the summer and losing heat during the winter. Louvres should be shading midday sun, but reflecting light off each other so that energy enters the building as light, not heat. Currently, the louvres are ineffective and have only been installed for aesthetic purposes, but could be modified.

Our recommendations to the client:
- allow the louvres to be replaced with correctly-angled light deflectors.

Lighting

On the whole, the lighting in the building is fairly efficient. However, there are lights in the basement which are on all the time as they are on key switches, and stairwell lights are left on most of the time. Light switching on each floor has been identified as being inappropriate for the depth of the rooms.

Our recommendations to the client:
- put stairwell lights on push-operated timer switches to reduce the time that they are on
- rewire lighting so that switches operate lights in groups, radiating from the windows inwards, rather than in lines from the darkest area of the room outwards.

Other electrical equipment

Appliances give out heat, even on standby, and contribute to overheating. The main problems are set out below.

Fridges

For the quantity of perishables that need to be kept cool, there are very large fridges in the building. Is a fridge required on each floor? Fridges become more efficient the more thermal mass they contain, so staff should be encouraged to keep bottles of water in the fridges to increase the fridges’ efficiency and provide cold drinks.

Vacuum cleaner

A 1000W vacuum cleaner is being used daily by the cleaner. This is unnecessarily high-powered. A variable-powered vacuum cleaner could be used instead, or the cleaner could be advised to vacuum when she feels that it is necessary, rather than every day.

Kettles

The coil-element kettles are used frequently, and would be better replaced by flat-bottomed kettles, which enable a single cup’s worth of water to be boiled if needed.

Computers

The policy of switching over to flat-screened monitors is good, but staff should be reminded to switch off equipment overnight.

Photocopiers

Your high powered photocopiers are using as much energy on standby as a printer uses when running. While it is running, it is using nearly as much as an electric kettle, but for much longer periods of time than a kettle is on. If the photocopier wasn’t used for printing it could be turned off for periods during the day. The third floor photocopier could be moved to more appropriate location, like ground floor where there are higher ceilings, so heat can rise above people.

You may be interested to know that the photovoltaics should produce enough energy to run your kettles, vacuum cleaner and fridges!

We would be pleased to discuss carrying out any of these recommendations, to return for more detailed investigation, or to present some of these findings to (company) staff.

Simon Lewis

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