zoning oil burner central heating

burdburd

i have a standard oil boiler - it has 3 zones upstairs rads, downstairs rads and hot water tank in the hot press. All 3 zones pumped via a single feed from the boiler and a single variable speed circulation pump. The 2 heating zones have motorised valves whereas the hotwater (hw) has no valve.

I have installed a 2 gang light switch so that i can manually turn heating on upstairs and/or downstairs by switching the pwr to the motorised valves - that's working fine.

now i want to add a valve to the hw zone so that after the showers in the morning i can turn off the heat to the hw tank. the Q here is if the two heating zones are turned off and i then turn-off the hw circuit - will my boiler blow up ?

I work at home and have the heat on quiet a bit - the plan is to zone all 3 areas and then add a multi-zone controller such as http://www.multizone.ie/

ideas, comments anyone ?

ircoha

The boiler stat should cut out the boiler before u burn out the pump

if the HW cylinder is well insulated, then the heat loss during the day will not be significant so it would not be necessary to put in the third valve.

Have u a stat on the tank or is the stat on the boiler determine the temp of the hot water?

If u use an Alpha pump from Grunfos the theory is that it will virtually shut down when all 3 valves are shut and then the boiler will cut out

youtheman

If you are going to put a third valve in the circuit then you should install an automatic bypass valve which is plumbed across the supply and return lines to your boiler. If all three valves close (which they shouldn't, assuming your controls are working correctly) then you have no flow, and you also have no way to dissipate the heat. Not good for your boiler (most probably sever water hammer). The bypass valve will protect you from 'dead heading' the pump.

On my system (gas boiler) there is a manual valve fitted across the inlet and outlets to the hot water cylinder. I don't have any actuated valves, but if I were to manually close all the radiators, plus the inlet to the hot water cylinder, then there is enough bypass so as I don't 'dead head' the pump (the valve is partially open).

You mention that your pump is 'variable speed'. I don't think it's 'variable speed' in the true sense of the word (via a frequency converter), i.e. your system doesn't control the speed during operation. You can ADJUST the speed during comissioning, but it's then set and doesn't vary. Of course, I could be wrong.

Oilrig

Automatic bypass valve... tell me more.

I re-plumbed chez oilrig, splitting the heating systems into two zones but figured that having both zones closed wouldn't be healthy for the circulation pump - hence have left the downstairs zone at a high temp.

I was planning to introduce a 1/2" bypass between the feed and return. Is there a more intelligent "automatic" option available?

JamesM

burdburd wrote: »

i have a standard oil boiler - it has 3 zones upstairs rads, downstairs rads and hot water tank in the hot press. All 3 zones pumped via a single feed from the boiler and a single variable speed circulation pump. The 2 heating zones have motorised valves whereas the hotwater (hw) has no valve.

I have installed a 2 gang light switch so that i can manually turn heating on upstairs and/or downstairs by switching the pwr to the motorised valves - that's working fine.

now i want to add a valve to the hw zone so that after the showers in the morning i can turn off the heat to the hw tank. the Q here is if the two heating zones are turned off and i then turn-off the hw circuit - will my boiler blow up ?

I work at home and have the heat on quiet a bit - the plan is to zone all 3 areas and then add a multi-zone controller such as http://www.multizone.ie/

ideas, comments anyone ?

If you have a well insulated cylinder, it will hold the heat and, if you don't run off any water, you will use very little extra oil, and won't need to shut off the circuit. I use the oil boiler, twice a day, all summer just to heat the water. The oil level barely drops at all.
You mention turning off all 3 circuits - just turn off the timer.
Jim.
I know that all seems simplistic - but sometimes too many controls can just be too much trouble.

burdburd

thanks to all for feedback....
I am not using stats in the rad zones, rather TSV on each rad;; I may add up/downstairs stats later.
I am going to add a cylinder stat and run wire back to boiler/controller.
The boiler has no by-pass circuit between boiler in/out flow. May add one as a precaution but this may effect the pressure in system when zone valves are open ?
The plan would be that each rad zone can independantly call heat based on a timer. The
hw zone will also call heat from a timer but also, when on, it will regulate using the cylinder stat.

In the event of all three timers being off/closed and the boiler failing to switch off I guess that's where the bypass route comes in ?

MickLimk

If you're going down the route of TRVs on all rads as well as a zone valve on the HW, then you certainly should install an automatic bypass valve.

Just think about the scenario where you're heating Zone 1 as well as hot water. Ok, the hot water cylinder reaches the set temp and closes the zone valve. Then slowly all rooms in Zone 1 reach the temp set by the TRVs and switch off. There is now no return path for your water from the boiler and the pump is still running because the Zone 1 valve is still open.

If you had a bypass valve installed, it would kick in at this stage due to the rise in pressure after the pump. It opens to provide a safe return path for the water back to the boiler which will quickly switch off due to the temp of the water on the return feed. Most bypass valves are adjustable so once you find the correct pressure setting for yours, it shouldn't affect the heating at all in normal operation.

Your alternative if you don't want to fit a bypass valve is to leave one rad in each zone without a TRV and fit lock shields on both ends so they can't be turned off.

burdburd

I now have a 3 zone controller (www.multizone.ie) with 3 x motorised zone valves controlled by 3 stats ( 2 room & 1 cylinder ). The next job is to provide some contigency by puting in a 1/2" bypass between the boiler flow and return with a manual valve that I can close down about half way - such that there will always be some flow in the event of a valve motor failing.

Pete67

This is what you need: Automatic Bypass Valve

The zone valves have an auxiliary contact so that the boiler can be switched on only when one or more valves open. It will normally be switched off when all the zone valves are closed. The Auto bypass valve ensures a constant head at each heating curcuit irrespective of how many zones are open. It also allows a return path to the boiler during the boiler cooldown cycle which is a feature of most modern boilers.

dingding

I have a similar system to the OP. I have 3 timers which energise motorised valves as necessary. There is a switch on the valve that closes when the valve is open. So when you energise the valve it powers the boiler and pump. It is not possible to power the pump and boiler unless one of the valves is open and there is a path for the water to circulate.

ballaghman

The question about the auxiliary is does it activate when the valve is energised, and would it still switch on if the valve was stuck closed, or is it the physical opening that switches the auxiliary. The bypass circuit with a manual valve is foolproof, but does affect pressure in the other circuits

Pete67

The physical opening of the zone valve switches the auxiliary contact, so it's failsafe - the boiler should not fire unless at least one zone valve is open. If the 3 zone valve aux contacts are wired in parallel, then the boiler will be enabled when there is one or more demands for heating upstairs, downstairs, or a need for hot water. The hot water zone valve should be switched by a thermostat near the base of the hot water cylinder set to 60 deg C. The heating zone valves should be switched by room thermostats in the appropriate locations. You just need to check the rating of the zone valve aux contacts, usually 5A @ 230 volts, and ensure that this is not exceeded. If necessary you can use a contactor to switch greater loads, but this would not be required in a domestic sysem. The auto bypass valve maintains a constant pump head irrespective of heating load, and also allows the boiler to circulate hot water during its cool down cycle (if required) when all three zone valves are closed.

burdburd

As a follow-up, I had a bypass with manual valve plumbed directly between the the flow and return. It is only open a turn or so - enough to let water circulate. It will reduce heating time but happy to have it there all the same. see pic attached which may help some visualise all this stuff. There is also a pressure activated valve that'll blow if required.

Have to say loving the setup as I work from home and in winter have heat on during the day - so with TRV's, zone stats and timer controls, I can really control the heating. It is great to know spare rooms are getting a squirt of heat to avoid stale smell (trvs) the HW cylinder only heats in the morning as required, upstairs comes on in all rooms before beddy byes where master bedroom is set to a desired 19 degrees using TRV, downstairs doesn't overheat during on sunny days when the south facing windows really heats thru the house (room stat in hall & landing) Kitchen TRV closes that valve as cooking is being done and if I light the fire in the sitting room, the TRV closes that room rad too.

No TRVs in bathrooms or Hall - those set to max flow as long as that zone is active. Also I put rad reflectors in each room where the rad was fixed to external wall - I like to feel that makes difference in heating time of the rooms

Just a couple of things with the installation, if the 3 bar blow off, blows off it will blow the electrics as your zone valves are below it and the bypass is normally after the pump to aid flow not before, Gary.

burdburd

Hey,

Do you mean that the blow off will wet the electrics and hence blow the motors etc. ? ....i.e. I should waterproof the electrics ...

I think the bypass was put ahead of pump in case pump seized/blocked the flow could literally bypass the conventional route.

JamesM

gary71 wrote: »

Just a couple of things with the installation, if the 3 bar blow off, blows off it will blow the electrics as your zone valves are below it and the bypass is normally after the pump to aid flow not before, Gary.

The bypass will actually draw the cold return water around the circuit again. It will flow in the oposite direction to your arrow.

It is easy to fit a length of copper to the safety valve and run it down to the floor area, or somewhere away from the electrics.
Jim.

I'm a typical manufactures engineer, good at bitching about other peoples work, not always so quick with an answer:D

burdburd

thanks for input.