Using a UPS instead of heat sink radiator

[cjw]

I was wondering if anyone had any experience of using a uninterruptable power supply (UPS) connected to the boiler recirc pump and CH pump instead of using a gravity fed heat sink radiator?  In my own application I don't really want to have a heat sink radiator above the stove as it's in the master bedroom and I'll also be using a thermal store that supplies the radiators as well as the domestic.  Is there any HETAS guidance on this?   My large bathroom radiator will not have a TRV installed and this is above the size required for the heat sink radiator, so in theory it will act as the heat sink radiator.  I will be installing an anti-boil stat on the pipe to the expansion tank to start the CH pump on detection of high temp (>90degC).

In my day job, as an engineer we use UPSs for certain critical operations that cannot 'fail safe' on loss of power (the majority of safety systems are designed to fail safe) and it's accepted within the industry I work in, e.g. environmental monitoring stations, trace heating of lines where the liquor will solidify when cooled or other detection and alarm systems that must be available at all times.

I can't remember off the top of my head, but the circulators are around 60W each.  My thoughts, based on my experience with my parents' WBS, is that it would take about 30 mins to get the fire to a controllable slow burn, assuming worst case that it's just been loaded with fuel prior to the power failure; so a 1000VA UPS will last about 35 minutes, which should be sufficient to either get rid of the heat or allow the fire to drop back.  I should add that I'm looking at worst case here as I will get a gravity flow from the boiler to the thermal store without the load unit but I think it would be better to have both connected. 

[Alan]

A ups, pump, motorised valve will not fail safe.

Even with tripple redundacy like used in fly by wire aeroplanes they will not fail safe.
You just reduce the probability of failure
Open vented gravity fed with the correct size pipe if the ball valve does not stick up on
The header tank then failure should go to plan.

Even this web site with UPS and cyclic redundancy keeps
Failing

Regards

Alan

[dhaslam]

If the store is big enough  it should be big enough to act as a heat dump on it's own.  My stove  wouldn't boil the  buffer tank even if was running flat out for a full day with the circulation pump off.   

[cjw]

A ups, pump, motorised valve will not fail safe.

Even with tripple redundacy like used in fly by wire aeroplanes they will not fail safe.
You just reduce the probability of failure
Open vented gravity fed with the correct size pipe if the ball valve does not stick up on
The header tank then failure should go to plan.


Even this web site with UPS and cyclic redundancy keeps
Failing

Alan,

I didn't suggest this design is fail safe, in fact I clearly stated that it wasn't fail safe. What I asked was if anyone had used this type of method because it's a recognised method in other industries in some safety critical applications.  Every system has a probability of failure, even 'fail safe' systems can fail dangerously, e.g. in the gravity system the heat sink radiator may be blocked by sediment or corrosion products, the valves may have been inadvertently closed, the radiator may be incorrectly sized, etc.

I compare the UPS usage to using a PRV in a pressurised system.  Both have a probability of failure on demand, but they are recognised to provide acceptable levels of reliability for their application; all I'm wondering is has anyone gone down this route?

As an aside, how many people actually maintain / test their PRV in the pressurised systems?  Personally I wouldn't like to rely on them after 5 or 10 years installation with no service.  At least the UPS provides some level of diagnostics to confirm it's functionnig, provided it's checked.

Dhaslam,

Agreed that the thermal store will act as a heat dump, but I'm looking at another layer of protection for the system to be sure.

 

[Solal]

Your system will  fail  safe without  the  ups.
Because...
A - It's vented
B - You have a heat leak radiator
C -You have a gravity  fed thermal store

Why do you want to go beyond accepted practise  and spend money  on something that is not needed?

I'm fitting a 40kw  log batch boiler (ksw i ksw plus) at the moment without any  heat dissipation arrangements  in the event of  electrical/electrical component failure.
(waits for the abuse)

[cjw]

Hi Solal,

Thanks for response.  In my original post I mentioned that I wanted to use the UPS instead of a heat leak radiator.

[Solal]

My large bathroom radiator will not have a TRV installed and this is above the size required for the heat sink radiator,

I was assuming this will act as your heat leak.

[Micol]

cjw - almost exactly what I'm thinking of doing.  I'll use an inverter (1700w Antares) plus 2 No. 12v batteries, intelligent charger (Stirling) on timer, plus changeover contactor on mains feed (inverter / mains to heating supply, plus turn inverter "on").  This should allow me to always run my heating (WBS with boiler and/or oil boiler) and will cope with the solar panels (in the future) and remove any stagnation problems.  It'll make me feel better / safer as well!  As I've got all of the main bits, it seems a good way to go.
Do keep us updated as to how you get on.

Micol