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Please critique this design



  • indevrede
    indevrede Member Posts: 33
    I thought I did this already

    I did a whole-house heat loss: 40k @ design day (with some envelope improvements). That means a 55k mod-con is sufficient, which is the most important question.

    I did a baseboard analysis: Three 50 ft runs. That means the radiation is oversized (good) and should match the design day load at about 130F avg temp.

    Any room-to-room or zone-to-zone imbalances will be handled in initial and tweaking, as will the ODR curve.
  • indevrede
    indevrede Member Posts: 33
    Please critique this NEW design:

    Set aside DHW for the moment. I've been chewing on this idea:

    Suppose it's 56F outside, so the total home heat load is 10k BTU/hr . Suppose also that the baseboard setpoint is about 110F, so each zone can emit 8k BTU/hr. What if each motorized zone valve opens in sequential order 1-2-3-1-2-3-1-2-3 etc? There would be overlap, so that, 75% of the time only 1 zone is open (8k radiation) and 25% of the time 2 zones are open (emitting 16k). So the average baseboard output is 10k BTU/hr, which matches the total house load, which matches the minimum boiler output. The boiler runs continuously, never shutting off, and no buffer tank required.

    Here are some hard numbers: zone 1 open for 3 minutes, both zone 1 and zone 2 open for 1 minute, zone 2 open for 3 minutes, both zone 2 and 3 open for 1 minute, etc. If desired, you could increase the valve open time up to about 8 minutes per valve, but longer than that the boiler would begin to cycle on and off.

    Now, what happens when the outdoor temperature drops below 56F? Then, the relative time 2 zones are simultaneously open increases. When it's cold enough, 3 zones have to be open at least some of the time to meet the load, and finally all 3 zones will be open all the time to meet a 24k BTU/hr total home heat load.

    To reiterate: from 10k to 24k BTU/hr total home heat load (between 56F and 36.4F outdoor temp) the boiler is never turned off, and the return temperature is exactly the same, about 110F. ODR setpoint is also constant.

    Above 24k BTU/hr heat load all 3 zones are always open, the boiler is always on, and the average baseboard temperature rises from 110F to 130F according to ODR.

    Below 10k BTU/hr heat load (i.e. above 56F outdoor temperature), boiler cycling is unavoidable, but the boiler fire-time would be about 10 minutes at 60F outdoor temp. Not bad!

    Now onto piping: I'm thinking the best way is with primary-secondary. The primary (space heat) loop would have a delta P circ and the secondary (boiler) loop would have a small circ set to constant rate, say 3 gpm, and control the supply temperature of the system loop (not the boiler loop). The delta P circ should automatically switch between 4, 8, and 12 gpm when 1, 2, or 3 zones are calling. The zone delta Ts would range from 4F up to 6.6F on design day.

    If you're still reading and interested, I'd pipe the DHW as priority off the boiler loop with its own small circ.

    So, the total equipment tally is: 3 circs (one of which is delta P), and 3 motorized zone valves. I also need some way to control the zone valves, which probably needs to feedback off outdoor temperature, or possibly boiler output (averaged over hours and possibly excluding DHW calls). I write control software for a living.

    What do you all think? I know I've glossed over zone and room balancing issues, I was just considering the whole-house perspective.
  • Paul48
    Paul48 Member Posts: 4,469

    I'm just not sure what type of windows you have to use to allow space travel.
  • remodel
    remodel Member Posts: 68
    55 will work

    55 will work nicely, radiation sounds good and DHW too.  You will get your ODR sussed in, the loch has some cool controls that you will be able to manipulate.  I plotted house load and ODR output v. outdoor temp to really fine tune my ODR but at the end of the day fin tube loves hot water...space travel next.  The posts are good, keep us posted as to how the install and performance goes.     
  • indevrede
    indevrede Member Posts: 33
    Maybe this has been done

    This snippet (image below) is from the brochure for the Honeywell AQ2000 series. "Zone synchronization" and "Boiler Short Cycle Protection" sound like what I'm proposing. Does anyone have experience with the AQ252 or similar?
  • indevrede
    indevrede Member Posts: 33
    OK, this is a controls issue now

    More googling. Tekmar TN2 does zone synchronization also. Not sure what their logic is, but I found this picture on their website.

    Anyway, the piping for this scheme will be the standard design that Lochinvar shows in the setup manual (P/S with priority DHW and zone valves). This zone sync stuff I introduced is really just a controls issue, so I'll probably post in the Controls category if I have any other ideas/questions.

    Thanks to all who chimed in. Some of you suggested zone valves and P/S piping, which I initially resisted but have now seen the light.

    Re: buffer tank, if I added one it would reduce the valve cycling rate, which would certainly extend valve lifetime. Need to weigh that against the cost of buffer tank + installation. Costs add up...
  • Paul48
    Paul48 Member Posts: 4,469
    Smart Money

    Would be best spent making sure you could heat the house with 130* water on design day. The output of the baseboards falls off significantly at that temperature. You need to make sure you have enough emitter in each room. I'd use the TRVs in sleeping areas, and let the ODR do it's thing handling the bulk of the home.
  • indevrede
    indevrede Member Posts: 33
    Any suggestions on cleaning baseboard?

    Good point. I'm basing my numbers off of a Slant-Fin chart that you can find on Google, but my baseboard has cheap-looking fin-tube that's old, banged-up, bent, and gunked up with dust and fur and cobwebs. There's no way it's currently going to reach the premium spec for BTU/hr, so I figured I would put in some elbow grease and spend a few days and try to really rehabilitate them. Any tips/tricks? Vacuum, toothbrush and pliers?

    Re: TRVs, all the bedrooms are on a single baseboard loop, so I can't do individual bedroom TRVs without added piping. Plus, I've abandoned the idea of TRVs so I can implement my "zone merry-go-round" control idea (aka space ship). Initially I'll use ODR exclusively, but if there are comfort issues then I'll add some temperature sensors and figure out how to make the zone cycling respond.
  • remodel
    remodel Member Posts: 68
    fin tube

    Heard some talk of fin tube being overrated by 15% .  The one thing I had a problem with was fin tube just does not give off that much heat at those low temps (at least that is what I saw) charts aside, so I would inherently short cycle, hence raising my ODR to some hot water.  Once I did that she would burns a lot longer.  Don't get me wrong on my low end I set her to 115° (with a large diff) water but she's going short cycle anyway (when it is 60° outside) so I get some condensing out of her.  Also study the onboard space ship controls real close (loch 55 smart control) they provide some similar stuff you were mentioning with the honeywell etc..        
  • Eastman
    Eastman Member Posts: 927
    zone sync

    The Tekmar system syncs the zones at the beginning of the cycle. The thermostats also provide indoor feedback to an ODR module, which adjusts the setpoint to match the loads at the minimum supply temp, and automatically adjusts the differential if required.

    The Honeywell system is probably very similar but I have not read up on it as much.

    As far as I know, there is no zone sync method that uses a hand off strategy, though. That wouldn't make sense if the system is in control of the supply temps and is allowed to adjust them to optimally match the emitters.

    It would be interesting to see someone install an indoor feedback system, they seem pretty rare.
  • indevrede
    indevrede Member Posts: 33
    "Zone handoff" sounds better than "merry-go-round"

    Zone-handoff. Has a nice ring to it.

    Thanks for the info on the Tekmar controls. Their diagram seems to show exactly what you describe and, as you pointed out, it's not quite what I want. (Actually, basically the opposite of what I want. Zone handoff evens out the total load over time, but "zone start-sync" intentionally bunches them together)

    I would add one qualification to your remark that this zone handoff strategy wouldn't make sense "if the system is in control of the supply temps and is allowed to adjust them to optimally match the emitters." ? The other requirement: a lot of mass, so when the individual micro-zones call for heat on a randomized basis they can somewhat average each other out, keeping the boiler from cycling by allowing the modulation rate to remain as low as possible.

    Installation should occur within the next couple of months, so this fall will be when I do the first real tests. I will keep you all posted.
  • Paul48
    Paul48 Member Posts: 4,469

    You are not going to get what you want at design day(or lower) temperatures, with the emitters you have.
  • indevrede
    indevrede Member Posts: 33

    I'm not sure what point you're trying to make.

    I'm not trying to be rude (I asked for critiques, after all), but are you implying I won't get as much condensing as I hope? That's true. But that fact doesn't change the piping or control strategy, just the ODR curve and my heating bills.

    No matter what supply temperatures I end up needing, if I implement this zone handoff strategy correctly, I will minimize cycling, maximize efficiency (because I'll be keeping the modulation rate as low as possible for as long as possible) and eliminate short cycling.

    Assuming I was going to get motorized zone valves anyway, the added cost will be almost zero (microcontroller+relays+24V transformer = couch change) plus I get to program and tinker with a control system in my own house. Win-win-win ? (As Michael Scott would say)

    Of course, there's still the possibility that the zone handoff plan has one or more glaring flaws and that I'll have to abandon it. See any?
  • ced48
    ced48 Member Posts: 469
    I've Found Water Temps

    below 120 degrees in slantfin, just don't seem to heat that well. I have been running nothing lower than 120, or higher than 140, seems to work well for me. I get run times of 1/2 an hour, or so, off maybe 40, 45 minutes. I know this isn't what the guys who want there modcons to always run like, but it works for me.

    I also think if you go with the TT 60, not the Loch 55, yo will have problems with the TT not modulating down enough-
  • Paul48
    Paul48 Member Posts: 4,469
    Pretty Sure

    That strategy falls into the "Six of one...Half-a Dozen of another" category. Based on the definition of a BTU, it should take the same amount of time to heat the water to a certain temperature, whether you are alternating zones, or feeding the home as a whole. I'll stop beating a dead horse about the whole system. I didn't reallize you only wanted to talk about control and stop-gap measures. Best Wishes
  • RobG
    RobG Member Posts: 1,850
    Panel Rads

    It sounds like you plan on staying in the house for some time and money does not grow on trees. As time goes on you would be wise to slowly change out the baseboard with panel rads and TRV's. If you do it one zone at a time, by the time you are done you can crank the temp down and run the boiler at true design temps. Panel rads operate at much lower temps and do not clog up with dust ( they look better and take up less space as well).


  • indevrede
    indevrede Member Posts: 33
    I was thinking that too

    Yeah, we just have pine trees on our property. All they yield is needles and branches on power lines.

    Any thoughts on Biasi Ecostyle radiators? They seem eco-nomical.
  • Eastman
    Eastman Member Posts: 927
    zone hand-off

    Zone hand-off is the opposite of what all these sync systems are trying to accomplish.  The goal is to prevent dispersed calls for heat and always fire into as much of the radiation as possible.

    A hand-off strategy could only make sense if the mod/con was forced to operate at a fixed setpoint.  In this case, even though the burner can modulate, the emitters can not, creating a mismatch between the house's true demand and the systems output.

    In a nutshell, it's better to fire 10k total into all the radiation all the time, as opposed to firing 10k into one zone at a time.  The latter requires higher setpoints, increases temperature swings in the zone, and reduces the connected load to the boiler which increases the cycle frequency.
  • indevrede
    indevrede Member Posts: 33

    I agree 100%. Thanks for explaining it better than I did.

    In my case (three 50ft baseboard zones), I plan to force the mod-con to operate at a fixed setpoint for total heat loads up to 24k BTU/hr (outdoor temps above 36F). Above 24k load, I'll allow the setpoint to rise so that the emitters can match the load.
  • Derheatmeister
    Derheatmeister Member Posts: 1,472
    Digital vs. Analog Anti short cycle program..

    I like the Idea of the Reverse Indirect/Buffer combination...This has been done before..I think here in the USA HTP has a product like this..

    I am a big supporter of Buffer Tanks for more that one reason ...Better fuel economy,Keeps the Boiler from short cycling which keep system components from premature failures i.e. gas valves and Blowers...Allows Air and Debris to settle out..

    Separates flow conditions which will not restrict the Boiler flow..If a sacrificial anode is part of that equation this can certainly not hurt...This would be a Analog system..

    If you are worried about Short Cycling with the LOCHINVAR i think that you may be able to overcome this somewhat via the Anti short cycle Program which is adjustable from 0 to 40 minutes ...They also have a Ramp delay which is a 6X6 control (6 Time spans with 6 modulation rates)

    I still think that a Tank is the real thing But if Room and Budget are a concern then the Digital version will also work ..Just not as efficient..... Then again one could argue the Buffer Tanks heat loss which could be 1 deg F/Hr depending on the Insulation/Ambient room temp and other factors..Hope this helps...Richard..
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited March 2014
    This thread is all over the place

    I love it...

    there are a bunch of companies selling panels in the US, pensotti and biasi are about half the cost of Runtal and buderus per BTU... I havent heard anything bad about any of them...

    although I think they rate them at 180, so really a 24x24 biasi says 4500btus but the panel is only 2700 at 140 degrees... a 24x24 buderus steel panel says 2500btu... Its confusing....

    some of the smaller buserus panels are on sale for around $50 each rite now, not sure how long they will last, I bought a bunch of them as I am sure others did also...
  • remodel
    remodel Member Posts: 68

    zone hand-off is a cool idea, but you might find that once the hand-off starts the other rooms cool down the hot rooms get hotter.  Even if you adjust setpoints, each area has its own dynamic.  I always thought something like this to would be cool if right at the end of short heat call a zone(s) could open and the boiler could dump some heat (btu/hr), say 5 minutes, then an zone opens etc... 
  • indevrede
    indevrede Member Posts: 33
    You're right, there really should be feedback

    Thinking through this some more, I agree with you that there could be comfort issues if the zone control is unaware of the zone thermostats. I'm still working on the logic, but it would follow something like: "If only zone A is being heated and either the supply temperature is about to reach its upper limit, or zone A's thermostat is about to reach its upper limit, then the zone controller should open the valve for the next coldest zone".

    Clearly the logic needs to be more complex, but you've got the right idea, the zone controller should intelligently wait to turn on and turn off zones according to the zone temperature and the supply temperature, to keep the boiler running as long as possible and as low modulation as possible. In some cases that logic might work out to evenly-spaced 1-2-3-1-2-3-1-2-3 calls (my original proposal), but more likely the timings would be irregular, the order might change, etc.