How should I set my delta T with a boiler bypass? I want it to be 40 degrees. So is it 40 degrees between the boiler temp and the return temp, or between the mixed supply temp and the return temp?

 

Set the bypass so the boiler comes up to temperature fairly quickly to avoid flue gas condensation. The delta T of the heating loop will constantly change according to the heat requirements of the house.

 

Wonder where rbeck has been? Haven't seen him in a while...

He would tell you to leave the bypass valve fully open, and begin closing the GLOBE valve that is between the boiler and the bypass until the delta T ACROSS THE BOILER is where you want it. 'Across the boiler' means just that, the return to the boiler, vs. the supply from the boiler.

 

I did mess with it a week ago. It seems I needed to adjust the valve on the bypass. I'm using a flow control valve on the boiler where the bypass on the return meet. I think the check valve in the bypass is creating enough resistance to force more water through the bypass than I want.

I think I'll have to wait probably another month before I can really get it set. It's still too warm to get all the radiators heated.

 

Why do you want a 40f delta-T in the boiler?
Do you have a boiler or system bypass?
If you have a system bypass you adjust the bypass and if you have a boiler bypass you adjust the boiler valve.
You have an ES2 with OD reset. If you adjust a larger delta T you will drop the system temp further since the sensor is in the boiler. I would think that a 40f delta-T in the boiler will cause it to short cycle with ODR. I would need to think about that more.

 

droopy, post the link to the before/after pics that you had in that other thread so we don't have to bounce around looking for them...

I'm not too sure you followed all the advice given at the time... IIRC it was said that you should not use a check valve on the bypass? and something about using a globe valve and not a ball valve? I could be wrong... but that's sorta how I remember it.

 

Before - http://flickr.com/gp/drooplug/66B98i
After - http://flickr.com/gp/drooplug/31nH93

I can take better "after" pictures if you guys would like.

I have cast iron radiators. I thought that a delta T of 40 was what is desirable in my situation. I installed a boiler bypass.

I tried setting the valves a couple weeks ago when it was still warm out. It really wasn't ideal conditions. I need to mess with it more and observe what is actually occurring when I adjust each valve when I am into the heating season.

I think the flow control valve I have where the bypass meets the return is causing a lot of resistance which forces more water through the bypass than desired. I could be completely wrong about this. I just need to wait for more appropriate wweather to make these adjustments.

 

Ok. I really don't know what to do now and could use some detailed explaining. I put the heat on today. I went into the basement to observe what occurs when the boiler runs etc etc. This is what I observed:

The current set point is 120 degrees. I recognize that when I have a bypass I will have to adjust my ODR so my return temp is not too low. I first tried running the boiler with the valves set based on what I did a few weeks ago when I ran the boiler to it's maximum set point. The current set point is 120 degrees. With the return valve all the way open and the bypass valve approx. 3/4 open, the boiler heats up quickly. When it shuts off the boiler over runs the set point by 20 degrees. If i open the bypass all the way, it makes this situation worse. I deduce from this that the flow through the boiler isn't enough.

I am really confused on what to do now. When the boiler fires, it hits the set point rather quickly. I want to avoid short cycling. So what exactly is short cycling? Is it just the burn time of the boiler? If so, what is the min. amount of time you want the boiler to fire? It does run a long time between firings.

rbeck:

Where is the sensor for the digital thermometer on the ES2? I notice that it was reading drastically different than the dial thermometer on the boiler tapping during my observations.

OT: Also, what is the difference between the es2 and series 3?

 

I ran the boiler again and I shut the bypass valve completely during the call for heat. even when I did this, the firing time was less than 2 minutes. My return temperature was below 110 as well when it reached a 130 SP. This is for my 2nd floor zone only. I'm going to run my first floor and see how that behaves.

 

I think I may have had an airlock at the flow control. Things are behaving differently. I didn't have much time to re-observe everything and I probably won't until next weekend. In the meantime, I would still like to know if a short cycle refers to just the firing time or not.

 

It is hard to tell from this photo but it looks like the bypass is a system bypass but the flow valve is not allowing a mix. The flow check is detrimental in this application as installed. You do not need the flow-check.
It looks like the pump is pumping away from the boiler but if that is the case the weight in the flow-check will not open. Unless it does not look like what I think I am seeing.

 

The pump is pumping away from the boiler. I put the flow check in based on discussions in my post about my piping changes. http://forum.doityourself.com/boiler...g-changes.html . It was suggested to install to prevent water from the DHW from flowing through the bypass. It is also suggested in figure d-w4 in appendix d of the manual. B&G say it can be used for a boiler bypass as well. I was not aware of the check not being able to be lifted in this setup.

It is a boiler bypass. Here is another picture at a slightly different angle. It should show the piping a little better. DSC00044 | Flickr - Photo Sharing!

To explain a little bit. The return water in that manifold flows from right to left. The bypass is on the bottom of the flow check. The return to the boiler is on the left. Continuing down the return towards the boiler, the DHW loop enters below that ball valve.

If you want any additional pictures, just specify exactly what you want a shot of and I will be happy to get it for you.

 

Well, it definitely appears that with the flow check closed, there isn't enough pressure to lift it up or all the way up. When I have the bypass open, the return temp is higher than the mixed water temp from my bypass and supply. I opened up the flow check and it changed all that. I took a shower this morning so it seems like it doesn't affect my DHW in enough of a way to cause a problem. I wish I understood this prior to buying that, but you live and learn.

Another question about return temps. I understand that the idea of the bypass is to send cool water past the boiler when the return temperatures are too low. But that doesn't raise the return temperature. It does raise the temperature coming out of the boiler. Even though my return temperature is low, will having my supply temperature around 130 or more mean my boiler is being protected from condensation?