Sanity check on older hydronic boiler setup

180 is usually the design setpoint in small modern systems.

is that a 50psig boiler? your pressure is high for a 30psig boiler but the height of the building might need something close to that pressure. some math shows that even if the highest emitter is 40 ft above the boiler you only need a little over 20 psig to reliably fill the highest emitter.

That delta T…if it's really only 5 degrees on a 280,000 BTU output boiler, it implies a flow rate of over 100 gpm… ???

You can get very accurate temperature readings by wrapping black electrical tape around the pipes and shooting the tape with a $15 IR thermometer. I've checked that method against a $300 thermal imager, and the $15 IR thermometer is within 1%.

On a 280,000 BTU/hr output boiler running a delta T of 5 F, that implies a flow rate of 112 gpm. In a 2-inch pipe, that's a flow speed of about 10 feet/sec. I'm not a pro, but a pro might say that's too high as above 6 ft/sec can erode copper.

So the low delta T and the high flow rate suggest you probably have a bigger pump than you need. Maybe not worth worrying about. On our smaller boilers we also had higher flow rates than necessary, so I reduced our flow rates by putting triac-based speed controls on the Taco 007 circulators. That slowed our flow rates from 17 gpm to 10 gpm, and raised delta T from 12 to 20.

The triac controls work on permanent split capacitor (PSC) motors. Don't know if that's what you have on those pumps.

if only a small zone is calling and you have a 280k boiler I would expect some short cycling and fast temperature rise

I don’t know that 1/4 hp circ is moving 100 gpm, 25- 28 gpm flow through a 280k boiler would be typical

There may be a pressure activated bypass on a 22 zone loop

so do we have any idea how it is piped to the apartments. are they 3/4" parallels off a 2" main. of course the ideal would be to get a zone valve in the line for each apartment but lot of work unless the building and chases were designed with accews to the takeoffs. if you did get control on a zone valve basis then you would want a variable speed pump with a pressure delta response. maybe a controller for the pump you have or compare the payback for a fancy **** wet rotor.

although i used a pair of smaller single speed wet rotor to replace a massive 1 HP dry rotor pump from the early 70s – it was a couple taco 011s iirc. they were in a modestly similar situation for 10 units that uses fan coils all parallel that used to have zone valves that have all given up and of course the thing wasn't made with any kind of modular rational way to replace 'em. removed all the zone valves and used a tekmar ODR, well a TACO PC702 which is a relabeled tekmar, that would handle your boiler staging and the system balances pretty well and the tenants can turn the fans on or up in the fan coils to compensate for comfort. you don't have the fans although depending on the extent of element and house furnishings you could have folks who are getting overheated on a relative basis swing some of the baseboard covers closed.

are the boilers primary secondary with their own pumps or serial or ?

I gotta tell you in figuring out the apartment balance with a single circ for the whole deal i'm real happy with the wifi thermostats so I can monitor the apartments simultaneously depending if you got signal in the building you can use although they usually require 3-wire setup so it depends what was originally installed.

the system i describe i ran 24/7 like a radiant floor. you'd still want some kind of averaging thermostat since you can't take your return too low with those boilers so you probably be fine on offing in 2 -stage fashion although in the NFN department we've been running through two staging atmospheric boilers on the steam side. if you're short cycling in shoulder season you could use two stage gas valves to go effectively make it a 4 stage setup.

Two pumps on this chart are the 1/4 hp model, either the 2-1/2 or the HD 3 theses are considered flat curve circulators ideal for zone valve systems.

Ideally a circ runs mid curve so you would be pumping 40- 60 gpm range. Those two boiler at 80% is 448,000 btu/hr available. So that 40- 50 gpm range seems about correct.

448,000÷ 22 units= 20,000 btu per unit heat. That would be about 40' of fin tube per unit??

A picture of the near boiler piping would show how the system is piped, where flow goes as zones close off.

If you are looking to make the system more efficient I agree the ODR control could maybe run the boiler at lower temperature for some, maybe much of the season.

An ECM type circulator would cut pumping costs by 50% or more.

There are many incentives available for converting to ECM circulators, and probably programs to have energy upgrades done. Find your state here.

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Don't get too hung up on delta T, it will be constantly moving in hydronic systems as the loads are constantly changing. This is an important condition to know. With 22 units that delta will vary quite a bit. The heat emitters driver the operating condition of the boiler, temperatures and ∆s

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staging the boilers would make a whole lot of sense. It sounds like the boilers are a bit oversized.

if you do odr you need to either limit it such that it doesn't fall enough that the return water temp doesn't fall below 130-140 or add return water protection to the boilers.

thats some pretty crazy near boiler piping. best i can tell the boilers are parallel on 1" for the near boiler except a 1 and 1/4 cross on the feed to the left hand boiler. i assume out of the picture on left hand boiler the pipe increase to 2" so this constriction is for short run but you'd have to have some serious velocity in that near boiler piping to handle 80% of the nameplate on those 2 boilers.

can't see where the PRV and expansion are connected so hard to tell if it is pumping away and that might also explain high operating pressure. with 4 stories I would always operate mine up in the mid 20s although i had the pumps on the feed so it actually would show 30 leaving the pumps for the system but would return with pipe loss around 25. so i had to charge the expansion tank up to accomodate and because it was constant on i didn't blow off the relief virtually ever even though i was theorectically close.

on the one hand parallel circ is going to cut down cold starts when calling the second boiler but usually i might see something like this as primary secondary. and you could cut down on your system pump while you would have to add boiler pumps. with modern pumps you'd spend some money but save electric.. doubt it would payback in electricity but if it contributed to better control and comfort for less energy could be worthwhile.

in a way though, those pictures demonstrate how almost anything will work cause it seems like its been that way for some time and aside from the balancing problem it works. still don't see any pictures and don't know if you have any access to see how this main manifolds to the individual units or if this 2 inch main disappears and returns but these unit connects are all hidden (and presumably not active by way of zone valves, nevermind say manual isolation valves if you had to work on one unit).

i doubt you're going into the unit by unit heat exchangers but if you want to use ODR with baseboard, you can't have enough fin. where I can i used the higher 'commercial' baseboard and put two runs of fin tube in it. but much of our hydronic insyallked base goes back to the days when they designed for 180 degree water to heat the place so they didn't even always put one full run of fin in each enclosure. when i started it was only my economic instinct that stopped me from doing that. it was almost the same price to buy enclosure and pipe as to buy enclosure and fin tube so i reckoned if a room was too warm they could just close the vents on some of the enclosure. in the end those places with lots of fin have proven much more resilient to ODR approach although the drop off in output is geometric not arithmetic. between that and having to guard return temps (something you could modestly ameliorate with a close loop primary secondary or storage tank) you don't get as much flexibility.

but not inconceivable if you are short cycling in shoulder season even with only a single boiler running to two stage those boilers.