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  1. #1
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    Frost Protection Regime Best Practices

    Hi guys, long time lurker and first time poster here!

    One thing that I've always pondered on, is best practices and suitable setpoints for frost protection regimes. I'm talking specifically about frost protection of pipework and plant here, and not internal building fabric protection as such.

    I'm not sure what the trend is across the globe, but here in the UK the typical advice is to employ a 'two stage' frost protection regime.

    • 1st stage. When outside air temperature falls below 2-3°C, open valves and bring on pumps to circulate water.
    • 2nd stage. When heating return temperature falls below 5°C, bring on boilers to heat water until it is around 35°C.

    The other bit of advice I've come across in the UK is to only allow the frost protection regimes above to take control when the building is out of its occupancy schedule. I've always thought that this could leave the system vulnerable, for example on the off chance that schedules might get set incorrectly by the user, etc. I would have thought that it be best practice to have the frost protection always allowed to kick in, irrespective of all other demands/schedules/etc. Thoughts on this? Is it normal/good practice to inhibit the frost protection whilst a building is occupied (irrespective of whether the plant might already be running or not)?

    Further, what vales and what pumps would you choose to run under stage 1? We've one system where the zone pumps and zone valves are all housed in an external, non-insulated plant room whose inside air temperature gets as cold as the outside air temperature, however one of these pumps feeds a heating circuit full of tubular heaters in a sports hall with no local valves to shut them off. Thus if the frost protection kicks in during occupancy hours on this circuit, and the boiler is on to serve other zones, the sports hall subsequently begins to heat up and up and up and result in some rather uncomfortable users. On the contrary, if we decide not to implement frost protection on this zone and associated pumps, do we leave those particular legs of pipework and assoc pumps at risk of damage when the temperature drops below freezing in that plant room?

    Lastly, do you typically monitor just the primary heating return for low temperature? Or would you suggest also monitoring all secondary returns too?

    Apologies for the long post! I've been struggling to figure out the best way to approach this for a while! I may be overthinking it, but I just don't want to receive the call to say that the frost protection didn't work effectively and now the client has a lot of burst pipes and damaged equipment!

    TL/DR. How do you guys implement your frost regimes?

  2. #2
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    There's a number of things here that are building specific:
    1. Is there water piping on exterior walls?
    2. Is there water piping in an area(s) with multiple exterior walls/excessive glass?
    3. Fire alarm sprinkler piping also needs to be considered.
    4. Boiler types - return water temperature you brought up along with the heating it up too, condensing boiler? Can the boiler(s) handle those temperatures without further negative affects?

    As to opening valves and such again I would only open up ones needed - cold areas/areas to likely freeze first.

    As to your plant room example, sounds like a poor design, but I would run the pumps no matter what during near freezing and below temperatures and do what you can to modulate the heat from the boiler to the sports complex - sounds like you need to up sell a mixing valve/primary secondary loop/heat exchanger. Not sure if you can monitor flow, but as long as your flow is not decreasing then your shouldn't need to add heat...but that puts a lot of reliance on a flow sensor working correctly, so hopefully you have multiple if you went that route.

    We monitor primary, secondary and space temps to try to give as much freeze protection as possible. Even gone to putting in extra sensors in 'odd' locations (fire sprinkler piping) to be able to alarm in likely freeze conditions. Also had to do numerous adds -monitoring return/mixed air temps as dampers don't seal tight and cold air falls down ductwork and can freeze things in the room, sink right under return, yet the room sensor was far enough away it didn't sense that as well.
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
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  4. #3
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    Thread Starter
    Quote Originally Posted by crab master View Post
    1. Is there water piping on exterior walls?
    On this particular site, not to my knowledge, although there is pipework within the aforementioned naturally ventilated plantroom that could be exposed to low outside air temperatures if the boiler plant wasn't running and subsequently heating up the air in the plantroom.

    Quote Originally Posted by crab master View Post
    2. Is there water piping in an area(s) with multiple exterior walls/excessive glass?
    Not to my knowledge, although the Sports Hall could well be a candidate.

    Quote Originally Posted by crab master View Post
    3. Fire alarm sprinkler piping also needs to be considered.
    We've no monitoring of the fire sprinkler system at all in this particular building.

    Quote Originally Posted by crab master View Post
    4. Boiler types - return water temperature you brought up along with the heating it up too, condensing boiler? Can the boiler(s) handle those temperatures without further negative affects?
    This particular system has a biomass boiler heating a buffer vessel. All heating circuits then draw from the buffer vessel.

    Quote Originally Posted by crab master View Post
    We monitor primary, secondary and space temps to try to give as much freeze protection as possible. Even gone to putting in extra sensors in 'odd' locations (fire sprinkler piping) to be able to alarm in likely freeze conditions. Also had to do numerous adds -monitoring return/mixed air temps as dampers don't seal tight and cold air falls down ductwork and can freeze things in the room, sink right under return, yet the room sensor was far enough away it didn't sense that as well.
    Good to know, how do you piece together your control logic for these frost protection scenarios in these cases? Is it a case of low temperature off one sensor then run all pumps and valves just to be safe, or do you run just the relevant pumps and valves for that particular heating circuit that was reporting low temperature etc.? Appreciate the thoughts!

  5. #4
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    You don't need monitoring of the fire alarm system, point with that is if you have a wet system and that piping runs thru an area that has a potential to freeze, then the surrounding temperature should be monitored for freeze protection.

    Piece it together by building walk thrus, looking at plans, talking to site personnel about past issues.

    I just run relevant circuits, if I can, but at times I've had to run multiple circuits to keep the boiler from short cycling/other.
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
    BIG Government = More Dependents
    "Any 'standard' would be great if it didn't get bastardised by corporate self interest." MatrixTransform
    My 5 yr old son "Dad, Siri is not very smart when there's no internet."


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