Old gravity fed boiler

Jsbeckton

Working on my EDR calculations and had a question. What should I use for the average water temp? My boiler is set at 180F but I don’t have any way of checking what it actually is. All I know is that after the system has been running for awhile the surface of the rads is about 145 at the inlet and 125F at the outlet based on infrared readings. What do you use for average?

Paul48

Don't focus on that. Here's the focus.....room "X" has a heat loss of so many btus at design. It has a 10' section of CI baseboard. Based on rated output for cast iron baseboard, I have to apply this temperature water to it to achieve the necessary btus at design. Save that info. On to the next room.

Gordy

Most charts have multiple water temps to base outputs on. As Paul says you need to find the water temp that will match the load with the existing edr in place.

Now part of the survey is to see how well matched all the emitters are at the same water temp in the system. Maybe an AWT of 160 will work for all. Maybe 150 will work for most, but some may fall short.

AWT (average water temperature) so if your supply is 180, and return 160 then 170 is the AWT with a 20 delta. That’s what the charts are based on.

Paul48

Your pictures show Cast rads, cast iron baseboard, probably a convector behind the grate, and you can get the rated output for all you have.

Gordy

Example:

Bedroom 1 has a heatloss of 6000 btu.

Bedroom 1 has a ci thintube radiator which has an output of 150 btus per sf of direct radiation with 170 awt.

Bedroom 1 thintube radiator has 40 sf of equivalent direct radiation.

40 edr x 150 btu = 6000 btus

This would be balanced radiation at 170 awt.

Now that’s an example. It could work out that maybe 160 awt will give the 6k output for that same room if the radiator is over sized.

Now to go further to see if the whole system is balanced radiation you would calculate using a starting point awt 170. If radiation in all rooms is over sized at that awt keep dropping the awt recalculate until you are balanced. Use this number for awt for the system.

Jsbeckton

Ok, so think I am making pretty good progress with these calculations but I wasn’t sure how to treat my kitchen since I have several types of enmities there (baseboard, blowers, radiant). See screenshot where I am getting AWT from 115F all the way to 165F.

Gordy

RElying on you’re edrs being correct. I would put the lower temp requirements on one manifold 7, and the other higher temp requirements on another manifold. I don’t know how this relates to their proximity with each other for home running like that.

The KHN can deliver up to 3 different temp requirements, and ODR curves for each. However it appears the boiler is not being replaced.

If not then using the higher water temp requirement is not a huge deal if you are going to use trvs, and the goal to get the lower return temps to make a mod/con more efficient. Another however is setting the system up for a replacement boiler in the future of a higher efficiency if desired.

Maybe there is other thoughts.

As far as the kitchen same applies you need to find the output of the emitters, and apply a awt that will satisfy the load.

Jsbeckton

The EDRs are kind of a best guess based on various charts that I found online that best match my rads. Is this typically what is done or is there a better reference out there? The only once I am absolutely confident in would be the baserays because they are new and the manufacturer has data.

Boiler was just inspected and they said it’s still in good shape and burning at 79% efficiency so was thinking there is no need to replace now.

The rooms with the low calculated AWTs are not near each other so does it really make sense to zone by that or should I stick to just splitting off the cooler rooms into a new zone? Also, all of the old rads have balancing valves that are not moving these days so I can’t really depend on full output unless I plan on removing all of those balancing dampers right? I am hesitant to do that becase they are all tied into the old steel pipe risers.

Gordy

ARE you entertaining the use of trvs.


I like to think about future scenerios.

Annasil

we have a conventional boiler with gravity fed hot water and pumped central heating. We are planning to have a new kitchen installed shortly. Someone from a kitchen company called today and mentioned to my wife that it would probably be in our interests to have a new boiler as our current one is (a) old and (b) floor standing in a corner of the kitchen. His comments were that installing a new boiler would free up some space in the corner and that, if he were to build around the existing boiler and it then packed in, access to it would be very difficult.

I understand that all new boilers now have to be condensing boilers and that these do not work with gravity hot water systems. I guess this would entail converting our system to a fully pumped system with motorised valves on both the hot water and central heating circuits. I also believe that we would need to install a cylinder thermostat and TRVs on all radiators except one, neither of which we currently have.

I'm tempted to turn down the idea because I fully understand how my current system works and where everything is. Upgrading to fully pumped will simply add more things to go wrong in addition to the fact that a condensing boiler would be far more complicated than my existing one. Also if we do need to install a cylinder thermostat this will involve running a cable from the central heating programmer all the way up to the loft where the cylinder is located.

Another issue is that, after we had a loft conversion and I moved my F & E tank further up into the roof space, the central heating system has airlocked on refilling every time I've had to partially or fully drain it. I've cleared the airlocks by fitting a hose from a mains cold tap to the expansion pipe above the F & E tank then pushing the air up through the bottom of the tank. To do that after upgrading would also involve manually opening the CH motorised valve (I think).

Could someone please advise whether I would in fact need to install a cylinder stat & TRVs? If not I might consider upgrading the system to fully pumped and getting a new boiler.

Gordy

Condensing boilers are not a must. However they do work well with gravity systems. Yes it will have to be pumped. That's the very short of what you are asking.

Tstat, or trvs. With trvs you have contrast each convector. But repiping convectors is a high probability. Depends on existing arrangement.

Ironman

IDK what you mean by a "cylinder thermostat". Are you referring to an old expansion tank at the top of the system? If so, that would be replaced with a new expansion tank near the boiler that's much smaller in size.

JUGHNE

Annasil, are you in the UK?
You should start your own thread, most here would be interested in your story. You may certainly follow this one in addition.