BREEAM Lift Credits – Part I
There are two BREEAM credits for lifts available and this article lets you know, in some detail, how you can about getting them.
There are two parts to getting your first credit and one part to getting the second credit. To make it more manageable we have broken down our explanation into three articles. The next two articles are:
Your First Credit
To achieve your first BREEAM lift credit you should be able to demonstrate an analysis has been undertaken of the lift transport demand, and of optimising the number and size of the lifts and the counterbalancing ratio of the lifts based on that anticipated demand.
This is what we call a Lift Traffic Analysis or a lift traffic study. The anticipated lift demand is modelled and/or simulated in a program to find the optimum number, size and speed of lifts you need in your building.
Can you do a lift traffic analysis?
Unfortunately probably not, unless you are particularly mathematically minded and diligent with repetitive calculations and have specialist knowledge!
This is because although, the basic theory and calculations are widely available, the calculations require an iterative process to arrive at the optimum solution; which is best performed by programs designed for the task. They also require some experience and someone that is proficient in their use.
Accurately modelling the anticipated demand on the lifts
- What percentage of people will use the stairs, if any?
- How does the lift traffic demand vary at peak times; during the morning, lunch time and evening?
- Which lift peak traffic demand is the worst (and should be designed for)?
- What type of lift traffic can be anticipated?
Types of lift traffic vary considerably for different building; offices, shopping centres and hospitals for example, and they all impact on the traffic demand on the lifts and hence the optimum selection of number, speed and size of lifts.
Unless your building is straightforward and you have a single or very few lifts then this analysis is best done by an expert who is adept and practised.
The output of a lift traffic analysis will give you some key information about how your lifts will perform, including a very accurate prediction of waiting times, journey times and the what percentage of the building population can be move by the lifts in a given time frame.
That is essential information for marketing purposes. Lift performance criteria is a requirement of many guidelines and Standards including CIBSE Guide D, Vertical Transportation Systems in Buildings and British Council of Offices Guidelines.
So a Lift Traffic Analysis helps you towards your first lift BREEAM credit and it gives you specific information about how your lifts will perform.
However, there is one further thing that needs to be considered.
What is a counterbalancing ratio and how does this affect things?
Electric lifts have a counterweight which weighs usually between 40% and 50% of the combined weight of the lift car and half the rated load. This is best illustrated by an example:
- Lift rated load = 24 person/1800 kg
- Empty lift car weight = 1200 kg
- Counterbalancing ratio of 50%
- Counterweight weight = half the load plus empty car weight = 900+1200 = 2100kg.
This means with the car half full the lift is ‘balanced’ and takes very little energy to move it.
Typically at peak traffic times, lifts are more than half full, but conversely out of peak times they can be less than half full maybe with a single person or a few people travelling in them. If you averaged the loading of the lift out throughout the day you would probably arrive at somewhere around half load, which, is why the optimum counterweight ratio is about 50%.
This is an almost universally held view, throughout the lift industry to such an extent that it is safe just to use a lift counterweight ratio of around 50%.
If the lift traffic load in the building is anticipated is particularly low, then you could use the 50% ratio and if the traffic load is high you could use a 40% ratio.
And that is it!
Two steps to the first part of your first BREEAM lift credit.