Boiler bypass with outdoor reset?

Vlad

Can anyone suggest how I should pipe my boiler so I can have hot water run below the default 140F using a Tekmar 256 on a converted (Gravity to pumped) system. House was build 1910 with cast iron rads and one zone of radiant. Boiler is a conventional cast iron (Lennox). Last work I had done was a 'home-run' system and the contractor put in a system bypass (main piping is 1-1/4", bypass is 1" with gate valve). I want to take full advantage of the bolier reset and I don't see that possible with keeping boiler min. at 140F. The system bypass seems OK sometimes (circulating water is cooler than boiler outfeed water), but I am afraid of condensing in warmer weather.

Weezbo

some things words fail to convey...do you have a picture ?

Vlad

Picture to come but question is how to pipe a boiler in theory

I will take a picture tonight and post. Presently there is a system bypass (Pump is on the water-out side of the boiler, bypass goes from after the pump to the return to the boiler. Bypass is 1", supply pipe to radiation is 1-1/4". As I said I will supply a picture. My question is, can a lower the "boiler min" setting on my Tekmar control to say 100F with this type of bypass and not risk condensing in the boiler? The alternative is to have a "boiler bypass", bypass that starts between the pump and the boiler and goes to the return. OR how should I pipe it to have the boiler always run above 140F but my radiation circulating water is lower as needed? I don't want to get too comlicated with things such as primary/secondary piping or adj. mix valves.

hydronicsmike

True answer, NO

A Bypass can never guarantee Boiler Protection. It can make it better, but never ensure Boiler Protection. The load can change (and therefore the water temperature returning to boiler) and your bypass wouldn't react.

True Full Reset below a Boilers minimum can only be achieved with Motorized Mixing. Boiler Minimum would still be 140°F. Mix System Temp would get full reset.

There are some guys who pipe a 3-way thermostatic valve into the boiler return, ensuring boiler return protection that way, while providing full reset to the system. However, this is a PI control you are talking about and it wouldn't really be a great scenario, nor would the control be able to properly operate the boiler if the boilers output changes considerably when the thermostatic valve changes flowrate past the boiler sensor on the supply by limitting the amount of flow available to the system. I hope this makes sense. If not, call me 250-545-7749, Ext. 214.

Regards,

Mike

Mike Reavis_2

The safe and cheap way to arrive at the answer to your

question is to get the boiler manufacturer to tell you how to pipe it given the design. Don't be surprised if they safe they won't stand behind it. Don't be surprised if you discover that primary-secondary piping by itself is not a sufficient scheme to adequately protect the boiler.

Mike

Vlad

Boliler manufacturer not in business

The boiler is a Lennox, they no longer make boilers or have an active phone number as far as I know. Talking to someone in a Hydronics store and also looking at Burnham literature, they show a "boiler Bypass" as described in my message above piped after the boiler, before the pump, it's supposed to be same size piping as main supply, but they put in a globe valve in the bypass to put in some resistance so your main flow always goes to your heating loop. To throw another 'wrench' in this mess, I still have the conventional room thermostats hooked up, except now into the Tekmar 256. Thus once heat demand is met, boiler shuts off. This should prevent long term run with low temp water.

'Another theory' Don't we have condensing happening 50% of the season when the weather is mild and the boiler only short cycles to maintain room temperature with water ~~90-110F? Because my system is a converted gravity system with large cast iron rads, my water temp requirement in the rads is low. I'd say my rads run 80-120F most of the season. Whats my best (least expensive) solution?

Vlad

Thanks for the lowdown.

Thanks for the rapid answer Mike, you wouldn't happen to work for Tekmar, would you? Perhaps I got the wrong control, but I thought I would create some comfort and save energy. But because my water runs so low (avg. 80-120F), will this control ever do what it's supposed to, unless it's really cold?
I don't need to gurantee non-condensing but if it works 80-90% of the time, I think it should be sufficient. This is a triplex and one tennat complains it's cold and the other that its hot and vice versa. One tennant sais that sometimes it's cold and sometimes its cold. He has a dummy thermostat on the wall and thiks it works, so keeps playing with it.

hydronicsmike@canada.com wrote:

hydronicsmike

Yes Vlad...

you can reach me at tekmar at any time. If you do not have a non-condensing boiler, we can get the Boiler Minimum changed. Please call me at your convenience and we will discuss options available.

best Regards,

Mike

Mike