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Making a Residential Boiler System Smarter

MichaelG
MichaelG Member Posts: 26
I'm a mechanical and controls engineer, but not an HVAC guy. I recently moved into a house built in 1777 which was gutted and added to in 1970, total current size is 2400SF. Over the years the 1970 HVAC components have been added onto with some additional disjointed systems, the result being a confusing and inefficient design. I have a fairly solid understanding of this entire system and it shortcomings, but am not necessarily familiar with what is available in the industry for improving the performance, efficiency, maintainability, and coordination of a system like this. My last house was Baltimore rowhouse with an ecobee3 controlling oil fired single pipe steam heat and a 16 seer 4 ton AC. It worked great, but this new house is a higher level of complexity for me. I would like some ideas for improvement.

Here is the existing setup...

Hydronic baseboard heat:
  • Oil fired Burnham boiler circa 2004, 120MBH
  • Four individual zones, each with their own circulation pump, 3/4" loops to slant fin baseboards
  • Boiler also heats the domestic hot water in a tankless setup w/ thermostatic mixing valve
  • The four circulation pumps are controlled by three Honeywell R845A relays and a L8124C1102 aquastat/relay.
  • Thermostats are all basic honeywell mercury, and I judge them all in need of replacement.
  • The age of the romex wiring to all the relays suggests this system dates to the early 70s. Some of the relays have a really old Honeywell logo on them.
Later updates to this home include:
2016: A 3 ton 15 seer heat pump to the upper floors of part of the house.
2016: A Mitsubishi minisplit system to the rooms not served by the aforementioned heat pump (3 rooms)
2017: A Hearthstone Shelburne 60MBH wood stove

Current issues with this arrangement include:
  • All the thermostats for the boiler are ancient, and don't display accurate temps
  • In winter, the boiler is the source of heat, despite the presence of the heat pump and minisplits. The minisplits are reportedly very advanced, but can't really be integrated to work with the other systems. The heat pump, of course, could be brought into the heating setup for the areas it serves, simply by installing a smarter thermostat
  • Shortly after buying the house, we had three consecutive days in single digits and the heating loop near the wood stove (which was doing most of the heating at the time) froze and burst several leaks.
  • The boiler control system is all very old relay logic
  • The aquastat has no concept of outdoor temperature

My question for you all:
What changes would you make to try to improve on the four points I mentioned above (performance, efficiency, maintainability, and coordination)?

Ideas I've had:
  • Try to more centrally control the boiler and its zone pumps, using something microprocessor controlled and with an outdoor reset, to save some fuel
  • Replace all the boiler zone tstats with wifi programmable units (such as the ecobee3 lite, utilizing FASTSTAT common makers to avoid rewiring)
  • Adding a thermguard on each boiler zone to ensure that the circulation pumps all run on a regular interval to avoid another flood due to frozen pipes
  • Putting the heat pump on the same thermostat as the boiler zone in that area of the house, and set an outdoor temp above which the boiler shouldn't be used
Additionally: Given the cost of energy now and into the future, does it make sense to leave the DHW system as is, in a boiler heated tankless arrangement? The alternative would be to add a tank, either boiler heated or more likely electric.

Thank you to everyone for your expertise and ideas!

Comments

  • mikeg2015
    mikeg2015 Member Posts: 1,194
    What your looking for is a bare bones BAS system. Could do it as well on a cheap PLC and HMI.

    I’m in your boat. I’m trying to coordinate 2 heat pumps with a steam system. I’m contemplating converting it to vacuum vapor and maybe add some zone valves when I downsize the boiler.

    I think I would use a hydronic zone controller for the boiler and make it a dumb heating plant. The use multistage thermostats in each zone to stage the heat pumps and/or auxiliary heat. Use heat pumps with outdoor temperature based balance point control for the conventional heat pumps.
  • Jamie Hall
    Jamie Hall Member Posts: 23,161
    edited January 2018
    If you take out the old mercury thermostats -- Honeywell T87's, the round ones? -- do me a favour. Pack them carefully, send me a PM and I will give you a personal address to send them to. They are bulletproof, and very hard to get -- and impossible to improve on. And I could use a few more...

    Now that said. There are a number of fancy controls you can add to that system, all of which will make marginal improvements in efficiency -- and no improvement in comfort at all -- at considerable cost and sacrifice in reliability. Not much you can do about the boiler; it is what it is. Utterly reliable, but non-condensing, so you are limited there in efficiency. You are also limited in terms of minimum return temperature, which limits the applicability of outdoor reset. However, you could use outdoor reset to lower the temperature settings in warmer weather. Just stay above condensing. You could also add a sensor or two as you mention to ensure that running your wood stove does not result in the boiler not running and and the heating pipes freezing. You could also add a lockout to prevent the boiler from operating when the heat pumps can carry the load. All good ideas.

    However, in terms of energy use... you mention the house was gutted and rehabbed in the 1970s, so any historic value it may have had is gone. Therefore, I would seek any and all ways to improve on the insulation and draught tightness of the house. They probably didn't save the original windows, so those 70s windows might be a good place to start on that. There are much better newer ones available now. Check your attic or roof insulation and add, if possible. Check the walls for insulation -- and for infiltration barriers.

    On the water heater, my own preference would be to use an independent oil fired hot water heater. Excellent recovery speed and good efficiency. However, if you want to go to peak efficiency and green, I recently installed a heat pump/electric combined water heater (not on any of the places I care for, though, thank you). They work very well, and provided you can live with slow recovery the electric elements never turn on -- and if you need fast recovery, the electric elements kick on and they are no worse than any other electric water heater.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Rich_49SuperTech
  • Dave H_2
    Dave H_2 Member Posts: 550
    If you are just looking at the electrical portion and not the piping, then you could use a single controller like a SR-504-EXP. Its a 4 zone switching relay for the circulators so all the wiring from the the thermostats and the circulators go to one central controller. The-EXP portion allows for the addition of the PC-700 which will add outdoor reset to the system. It also has some settings that can be adjusted for circulator exercising; once a day or once every two weeks.

    However, having your hot water in the coil does limit the outdoor reset option. You could separate the DHW by either adding a new hot water heater or an indirect tank to stop the boiler from maintaining a high temperature and put it on cold start.

    If you get into repiping the boiler, then you can change it from zone pumps to zone valves with one variable speed circulator that responds on temperature drop across the boiler.

    Dave H.
    Dave H
    Rich_49Tinman
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    If the existing thermostat's don't read accurately they are probably not level on the wall or an air draft in the wall coming through the wiring opening
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    The thermometers on those old thermostats can all be recalibrated with a small screwdriver.
    Since you would be advised not to use short term setbacks on a hot water system, the lack of programmability should not be a problem.—NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,161
    Hey guys, don't discourage the man. If they're the old mercury ones, I want one or two of them!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Zman