A STOPPED CLOCK IS RIGHT TWICE A DAY
The need for ventilation in our home is as variable as our use of it.
- We go to bed and sleep, wake up and go to work.
- Our homes are busy one day and not the next
- Our families grow and shrink
- Our buildings change over time.
Our building standards must guess a number, a demand, for all occasions. Big or small, busy or not. It’s called the whole house ventilation rate. And this is the number most systems should be set to and are assessed by.
Set that number too high, and we over-ventilate our home, wasting energy,
Set that number to too low to save energy, and we increase the amount of time we under ventilate, and air quality deteriorates.
A stopped clock is right twice a day, and a fixed ventilation system will be right for a brief moment in time as the demand meets that supply and then…..
Step in Demand controlled ventilation.
Demand-controlled ventilation follows ventilation demand by measuring air quality and adjusting the amount of air that moves in or out of a room or building to follow the need, never over-ventilating, and always meeting demand.
A meta-analysis of 38 studies of various demand-based ventilation showed that ventilation energy savings of up to 60% can be obtained without compromising IAQ-even sometimes improving it (Guyot, Sherman, Walker, 2017).
That sounds great, but if I don’t know what flow rate it should be set at, how do I know it’s enough?
First, you need to be sure that the ventilation system that decides how much air you are getting is based on sound principles, the sensors it uses to measure air quality are accurate and conform to standards and that it works for you where you live and the kind of house you live in.
This is particularly important if the system decides to lower flow rates below those set in building regulations, as you want to be sure when doing so, it doesn’t put the occupants or building at risk.
In most countries, this is done through an agrement process. Why?
While the products might be broadly similar from country to country, each country will have different building types, weather, regulations and requirements, and this means that even from the same manufacturer, there can be differences in how those products are set up to perform to meet those requirements. This is why practically it is found that it’s best controlled by local agrement.
A number of ventilation standards and national regulations have progressively integrated an allowance for DCV systems in residential buildings. (Typically through agrement). Simultaneously, energy performance regulations include the opportunity to claim credit in energy calculations for savings from such systems.
In Europe, several countries enable the use of DCV systems, including Belgium, France, Spain, Poland, Switzerland, Denmark, Sweden, the Netherlands, and Germany (Savin and Laverge, 2011 ; Kunkel et al., 2015 ; Borsboom, 2015).
DCV strategies have been used at a massive scale, notably in France and Belgium, for over 30 years. As of August 1st 2016, 23 DCV systems in France, 34 in Belgium, and 37 in the Netherlands have received an agrement. Most of them are humidity or CO2-based strategies.
All of them are approved locally, with specific characteristics for approval that suit local buildings’ weather conditions and building standards.
That’s not to say there are not alternative ways of demonstrating compliance with regulations other than through Agrement or demonstrating efficacy by other means.
However, unless everyone is measured against the same set of rules, like those set and assessed by an organisation like a standards authority, it can become tough for lay persons to understand if the efficacy of a product is based on, for example, local conditions or houses in Spain!
This Agrement was approved by the NSAI in 2019 after several years of working with building standards and other state bodies to determine the correct set of assumptions and rules that would apply.
That included a model for assessment that looked at
- House types
- Weather conditions
- Occupancy profiles
- Ventilation characteristics
- Thresholds and benchmarks that had to be achieved.
This Agrement now lays the basis for how this system is assessed under the building regulations and significantly simplifies the process of approval of the system under the third-party ventilation assessment, which is a requirement of the building regulations.
Without it, the testing gymnastics required to fit a variable volume system into a fixed ventilation assessment methodology leaves loopholes and grey areas that don’t serve the industry and consumers well and can lead to confusion in the marketplace on the actual performance of systems in Irish homes.