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Member questions: domestic cold water and air change ratesJanuary 2016


Jayne Sunley, Information Manager

Written by Jayne Sunley, Information Manager, BSRIA

Q1. In a long term residential build project how do I avoid issues with domestic cold water services while homes are empty? I’m concerned that CWS tanks and pipework will not get the required turnover, what are my options?

The best protection against water quality and corrosion is quite simply to get the properties occupied sooner rather than later. But if you must keep the properties unoccupied then be aware that stagnation in cold water services causes particular problems for copper tube and can lead to rapid pin holing. There is a difficult choice between:

  1. keeping systems dry until occupancy which precludes conventional pressure testing
  2. filling with water that will require regular flushing through outlets

Regular flushing prior to occupancy is time consuming and may be difficult in residential property due access issues and not guaranteed to avoid the problems. Keeping the system dry means the complexities of gas pressure testing and some leakage issues not being immediately apparent.


Q2. What are the target air change rates for large retail units? CIBSE Guide A suggests 2 to 4 air changes per hour but this seems too large?

CIBSE Guide A’s figures are correct but it is important to consider that these are just benchmarks or recommendations for air change values. It is important to consider that the air change rate adopted for a specific project will need to be compatible with the overall design concept. This will include issues such as energy targets which may have an impact on the amount of air that can reasonably be provided to the space. Also, it may be more appropriate to look at how much fresh air would be required to achieve a particular level of internal air quality rather than to just apply a general air change rate figure.


Q3. How often do fire dampers require maintenance?

BS 9999 requires that the absolute maximum interval between checks is two years – however a risk assessment based approach may require shorter intervals for dampers protecting escape routes and sleeping areas, or where particularly dry environments may lead to obstruction of operation.


Q4. What are the reasons a CHP plant could be used over a biomass boiler for a residential care home in a remote area?

You can meet the whole heating load requirements with a biomass boiler but if deciding to opt for a CHP it would still have to be a CHP plus boiler as the CHP sizing is limited by the base load heat demand (mainly hot water) and a boiler is still needed to meet the peak demand.


Q5. Are there any regulations or best practice for the recommended surface temperatures for radiators in residential buildings?

The NHS Estates guidance Hot Water and Surface Temperatures as well as the HSE’s Managing the risks from hot water and surfaces in health and social care gives guidance on surface temperatures for residential care homes and social care properties with the recommended surface temperature not exceeding 43oC the guidance also makes further recommendations such as low surface temperature heat emitters as well as guarding heated areas with measures such as radiator covers.

However, the guidance seems to be limited to health and social care properties. There are no specific guidelines on radiator temperatures in commercial, public buildings or private dwellings. The surface temperature of a radiator is generally assumed to be the temperature of  the inlet water, so in a boiler fed central heating system temperatures from 60oC to 80oC are not uncommon. With alternative heating systems, solar or heat pump fed, the temperatures could be significantly lower.

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