Grey area in grey water

Chiller condensate wastewater is grey water, all grey water is carried in a sanitary pipework arrangement connected to FW drainage system installed to the relevant Building Regulations.

Recent events have brought refrigeration drainage issues into the spotlight, regarding maintenance, health and safety standards and liability. A recent prosecution has effectively changed the priorities for retail drainage ? the Health and Safety Executive clearly identified the failure and who was responsible, with the judge ruling that “Maintenance issues should be identified and addressed at management level.”

This in turn raises the broader issues of compliance in the application of industry standards to HVACR drainage, and the resulting liabilities in the event of a Health and Safety prosecution.

Neither the British Refrigeration Association, or the Institute of Refrigeration offer any guidance on the subject of HVACR drainage, despite the fact they accept the overground drainage to be remit of the installer/maintainer. ASHRAE does offer guidance for condensate drains, using the International Mechanical Codes (307), for HVACR drainage, (Adopted by the Building Code Council)

Here in the UK we have the option to use the IMC, or, the more detailed, and appropriate Building Regulations which cover all indoor gravity drainage prescribing the British Standards Institute -BSEN 12056. The irony is, that in many installations, both are ignored, and overground refrigeration drainage runs flat to the floor without any slope whatsoever.

The laws supporting compliance standards, and used in the event of any prosecution, are The Workplace (Health, Safety and Welfare) Regulations 1992 Reg 12, The Health and Safety at Work etc Act 1974 (HSW Act), The Management of Health and Safety at Work Regulations 1999.

 Building Regs are designed primarily for the health and safety, welfare and convenience of the building’s occupants and for energy conservation. 

Approved Document H of the Building Regulations covers drainage, this drainage should minimise the risk of blockage or leakage; be accessible for clearing blockages; and be designed in such a way as to prevent foul air from the drains entering the building. No slope in a condensate drain does cause blockage, and the growth of biofilm jelly, slime identified in the prosecution as the factor responsible for the blockage.

How the drainage water is moved in food retail, this will be one of three ways:

? Vacuum (less than 1%)

? Pumped (Less than 3%) 

? Gravity (Around 97%)

Gravity systems are by far the most popular in food retail, but all methods depend to some extent on gravity drainage that is subject to the statutory legislative requirements. 

Vacuum drainage system - inside building, conforming to BS EN 12109

Vacuum drains use differential air pressure (negative pressure) to move the grey water. A gravity drain carries wastewater down to the collection chamber. As soon as the level reaches a defined height, the vacuum interface valve opens, and the negative pressure sucks the wastewater into the vacuum sewer main.

Thus, in food retail, vacuum drains are still to some degree, dependent on gravity. They are often laid flat to the sales floor beneath the chiller.

Pumped system - conforming to BS EN 773

Here, condensate pumps move the grey water using centrifugal, or piston compression pressure to force the grey water from the sump collection point to the store’s main foul drain. Again, to some degree this is dependent on gravity, as the condensate overground drains must run to the collection sump. These drains are often laid flat to the sales floor beneath the chiller.

Gravity system

Gravity drains depend on a slope from the source to their destination for their effect. The gradient for any indoor sanitary gravity drainage should be between 1.8% and 9%, and drains depend on that flow to keep themselves clean.

Gravity drains are designed to maintain a self-cleansing velocity (i.e. a flow that will not allow particles to accumulate), which is generally obtained with a minimal flow of 0.6-0.75 m/s

A constant downhill gradient must be guaranteed along the length of the drain to maintain self-cleansing velocity. If that required slope cannot be maintained, then a pump must be installed.

These are the basic legislative standards for indoor gravity drainage, but the standards also dictate that the connection between the overground drains connection to the below ground drain MUST be sealed to prevent leakage, and odour venting from the drains. 

 Any gravity drain running at less than 1.8% slope, for whatever reasons, is non-compliant by industry standards.

Commissioning of HVACR drains

The water seals of sanitary appliances should be fully charged and tested: Air pressure equal to 38 mm water gauge should remain constant for a period of not less than three minutes.

Maintenance of HVACR gravity drains

The legislative standard requires that access points should be provided to give access to any lengths of discharge pipe which cannot be reached by removing traps. (BS EN 1566-1) Pipework should have a minimum 1.8% slope, (18mm per metre), and all connections should be sealed.

Biofilm

We know that the standard of drainage is a factor in the growth of biofilm EPS (jelly) in condensate drains ? drains with no slope allow the static ‘dead spots’ that suit microbial growth. Ensuring that the drain has a minimum slope is not a guarantee that there will be no biofilm problem - but it will certainly reduce the possibility.

  PPM

It is clear that due consideration of the issues in maintenance and compliance will be important when both designing and installing the drainage for food retail – It is perhaps surprising then that there is currently no industry guidance covering the drainage aspects of a chiller installation. 

Installations that are optimised to reduce condensate blockages will help prevent further problems for the retail store, such as water leaks, while reducing the number of maintenance callouts. 

Duty of care

Who does the duty of care lie with?

It lies with all those involved: the designers, specifiers, installers, OEMs, retailers and contractors.

 If the refrigeration industry cannot endorse the standard as relevant to HVACR installations, the trickle down effect impacts heavily on any installation for all the stakeholder group. 

 A basic standard to work from, as a starting point, needs to form the foundation for design, installation, operation and maintenance, this will establish a solid point of reference from which all in the stakeholder group can clearly define remit and responsibility, and support the delivery of compliant, efficient and cost effective installations.

Gel-clear manufacture a range of retrofit drainage solutions. Pipe support, condensate drain tablets, and header drain connector, all low impact solutions to resolve the biggest HVACR drainage problems on existing refrigeration.

Paurick Gaughan