Radiant floor from off the grid to on the grid, help with changes

Discussion in 'HVAC Heating & Cooling' started by Chuck, Nov 14, 2019.

  1. Chuck

    Chuck New Member

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    Nov 14, 2019
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    Biologist
    Location:
    Youngsville, NM
    Howdy folks, new DIYer here from northern NM. This is a great forum that I have been watching for years, now I need a little advice.

    I have an adobe home that is currently off the grid and has been since 1999. I am bringing in power to make it a grid-tie system. Being off the grid, I have a 48v system with 8 Rolls batteries and two large inverters. I have 24 panels that charge the batteries and a generator when needed. The house is all standard wiring, running through the inverters. Some systems, like my radiant floor, are a little odd and I need advice to get them converted.

    My current radiant floor has 2 circulating pumps, one for the front and one for the back of the house. These are 24volt pumps that barely push 3gpm. The water is heated with a tankless Noritz combi boiler (CB-199-DV-LP) running on propane. I have a weird proprietary system someone installed that turns on the pumps and boiler from the input from the t-stat in the house.

    So the 24volt pumps will be going away, replaced with standard 120v pumps. The proprietary wiring goes away. I'll need some sort of pump controller that gets notice from the t-stat to turn on the pumps and let the boiler know to turn on. This is where I need the advice on whether or not I need this pump controller, what kind I need, and whether or not you think a water storage tank would be good to add to the system or not. There are zone valves in the house, but the old wiring is jacked up and I've never used them. The radiant is either on or off for the front and back of the house. To get the zone valves to work would require new t-stat wiring and with adobe that's a pain.

    Thanks for any advice. Chuck...
     
  2. Dana

    Dana In the trades

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    Any 120V zone controller designed for pumps or zone valves also has an output to call the boiler and power the pump(s) when any zone or zones thermostats are calling for heat.

    Is your heating system plumbed primary/secondary, with closely-space tee type hydraulic separator, as shown on p.31 of the manual? Did they keep the 120V internal pump driving the primary loop, or did it get swapped out for a 24V version, wired it separately/externally? Or is it pumped direct, with 100% of the radiation flow going through the boiler?

    To figure out whether or not a buffer tank is needed requires a bit of analysis. Since you have a heating history on the place, using EXACT fill up dates and amounts correlated with wintertime weather data it's possible to accurately infer the design heat load using this methodology.

    Then one has to figure out the heat emission rate for each zone at the temperatures the system is running relative to the minimum firing rate of the boiler. (In this case a relatively high 17000 BTU/hr-out.) If starting from scratch using this napkin math would be in order, but since you have a functioning system simply timing and counting the burns & intervals is probably a better approach. As long as the minimum burn times are 3-minutes or higher when serving any single zone, and 5 burns per hour it's probably going to be OK without a buffer tank. If it's delivering a dozen 45 second burns per hour something needs to be done, some if which may be tweaking the programmable parameters in the boiler, increasing the operating temperature to increase the heat emittance from the radiation, combine some of the zones into one for higher emittance, or as a last resort, add a bunch of thermal mass in the form of a high volume hydraulic separator (like Boiler Buddy) or a straight-out buffer tank.

    Then what is the in-to-out temperature you're seeing with the pumps that "barely push 3gpm". A flow of 3 gpm is 1500 lbs/hr. At a delta-T of 10F (120F out, 110F back) that s 1500 lb/hr x 10F = 15,000 BTU/hr. A 20F delta-T would be 30,000 BTU/hr, a 5 F delta-T is only 7500 BTU/hr (and likely to be short-cycling the boiler, since it only modulates down to ~17,000 BTU/hr .)

    Is that 3gpm through the tankless, or 3 gpm through some zone or another, or when all zones are active or... ?
     
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  4. Chuck

    Chuck New Member

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    Location:
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  5. Dana

    Dana In the trades

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    The boiler is plumbed with a t-type air separator as shown. The pump inside the boiler was not changed out or even used I don't think.

    I'm not sure what the t-type air separator is referring to.

    If the internal pump isn't used there has to be an external pump driving the flow. Pictures of the system as-is might be useful.

    The boiler seems to run constantly on the low setting to maintain the radiant water to 105.

    Is it keeping a buffer tank (also fed by the solar) at 105F, or...?

    The heating water from the boiler splits into two pipes, each one with a 3 gmp 24v pump and then both returns come back and go into one pipe back into the boiler. That is the best I have on that.

    I'm pretty sure that a steady 3 gpm + 3gpm = 6gpm would be more than the boiler can handle long term without eroding the internal plumbing. If it's plumbed primary/secondary with 3gpm through the boiler (at some delta-T) and 3 gpm through the radiation ( at a different temperature) that might work. I suspect your system architecture is plumbed primary/secondary roughly like this (but with only one zone pump, not five):

    [​IMG]

    How do you know the pumps are delivering 3 gpm? Care to share the model number(s) of those pumps?
     
  6. Chuck

    Chuck New Member

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    Hi Dana,

    The diagram that you posted is what I have, except I have 2 zone pumps, not 1. One of the zone pumps is an El Sid 24v pump with a max flow rate of 3.3gpm. That’s on the smaller zone at the front of the house closest to the boiler. The 2nd zone pump doesn’t have a name but it’s also 24v and slightly larger. I’ll try to attach pictures. It supplies the back of the house which is a lot larger.

    I don’t know if it has a small buffer tank inside, it may. It’s not fed by solar, just the 2 returns from the radiant.

    The Noritz spec sheets say it can handle up to 9gpm depending on the heat rise.

    Once I switch to grid power, I would just call up the local HVAC and have them help me but I’m a 2 hour drive from the nearest companies. It’s tough to get help when you’re out in the sticks.



     

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  7. Dana

    Dana In the trades

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    I don't clearly see the closely spaced tees, but if plumbed that way the primary/boiler loop is being driven by the 116 watt internal Kiturami pump.

    Per the manual the 9 gpm is the max rated flow for the domestic hot water side not the heating side. It would take a HELL of a pump to actually deliver that through the high pumping head of the water tube heat exchanger, and pumping 9gpm at the duty cycle of a heating system would probably kill the thing in one heating season. I'll bet you can't get that much flow out of the domestic side unless you have unusually high water pressure from your potable water system.

    The heating side flow is shown by the pump curve on page 27. If installed on a high-head system and pumped direct it could be 1-3gpm. If it's plumbed primary/secondary with fairly short runs to the closely spaced tee hydraulic separator (page 31) you're probably looking at 4-5 gpm.

    So now you're looking for suitable 120VAC replacements for the 24V zone pumps that won't over or under-pump the zone radiation.

    The El Sid SID10B24 (is that the model#?) is rated 3.3 gpm max (at ~1-2" of pumping head, not 1 foot), but delivers a reasonable ~2 gpm @ ~3' of head. If it's delivering the heat reasonably with the existing zone plumping it's enough pump, and you probably don't want to bump up the flow by more than 2x. The pump curve is found in this document.

    That curve is comparable to (only slightly wimpier than) the Taco 003 , or the (high efficiency ECM drive) VR1816 on it's lowest fixed speed setting:

    [​IMG]

    ^^Tac0-003 curve is the lower left ^^

    [​IMG]
    ^^VR1816 in fixed-speed mode^^

    A single VR1816 operating in constant pressure mode or a Grundfos Alpha 2 in auto-adapt mode could replace both pumps, if one switched over to a zone valve solution:

    [​IMG]
    ^^VR1816 in constant pressure mode^^
    [​IMG]
    ^^Grundfos Alpha 2 curves^^


    Is there any sort of brand marking or logo on that other pump?
     
  8. Chuck

    Chuck New Member

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    Biologist
    Location:
    Youngsville, NM
    The internal Noritz pump doesn't run as best as I can tell. If it did, the flow rate for domestic would be constant right? The flow rate varies as the pressure tank drops and then refills with the well pump. When the radiant is called on the two 24v pumps start up right away. They will pump for a minute or two before the boiler will fire and start heating the flow. The internal pump doesn't work there either.

    The 24v pump you asked about seems to be a March Pump 809 series based on the part number. However it's almost 20 years old. The El Sid is only a few years old because I bought that and installed it. The old wiring for the 4 zones is all bad and doesn't work. Unless I run all new wires, which I don't plan to do, I'll be abandoning the zone valves in place.

    I'll work with a local installer if I can find one to get a new circulation pump to replace the two 24v pumps. I'll get a boiler buddy tank to help with the duty cycle and I'll get a new controller to make all this work.

    Thanks.
     
  9. Dana

    Dana In the trades

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    Rong (as in "not right").

    The pump is on the heating side of the combi, not the domestic hot water side, and would only run when there is a call for space heating.

    Have you verified that? If so, how?

    In your response (#5) you indicated that it's plumbed like the diagram in response #4. If both 24V pumps are zone pumps and the internal pump isn't running, there will be nothing driving flow through the boiler,and the system simply doesn't work (at all).

    If the combi boiler has been hacked to run the primary with an external pump, is the internal pump even still installed? If yes, wiring it back up the way it was shipped would replace the primary loop pump.

    Manually opening the zone valves and operating it as a single zone system (which it sounds like you've been doing?) is fine as long as the room to room temperature differences are reasonably bounded. From your prior descriptions it sounded like you had only two zones, with one pump per zone. It's worth figuring this out before buying any new hardware.


    If it's pumped primary/secondary it takes a minimum of two pumps, one to run the primary (boiler) loop the other to run the secondary (radiant zones) loops. A single-pump solution pumping direct (not primary/secondary) may exist, but there would be some math involved to properly specify that. If operated as a single zone it's likely that a Boiler Buddy would not be needed. If pumped-direct a Boiler Buddy is definitely not the right solution, since the Boiler Buddy is designed to be the hydraulic separator between primary & secondary loops, not just a simple buffer tank.

    Take the time to trace out the plumbing and verify whether it's being pumped primary/secondary (probably is, but I can't tell from your pictures.)
     
  10. Chuck

    Chuck New Member

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    Biologist
    Location:
    Youngsville, NM
    Thanks for correcting me on the internal pump. Also, I guess that I haven’t verified that the pump doesn’t run during heating but based on your description that it wouldn’t work at all then I guess that it does run. The boiler has not been hacked at all.

    I do have two zones and a pump for each. The additional valves for each room’s control are not currently wired in. I’m operating those manually as you stated.

    My big gripe is that when the radiant is on the boiler is always on. Even though it’s super efficient, it’s minimum BTUs are high enough that it adds up to a lot of propane. I was hoping to have a hot water tank of some kind worked into this system where the boiler would heat it up as needed and then shut off while the circulator pumps run in the meantime.

    I can’t find my install pictures for the boiler and right now it has my water filtration gear is sitting in front of it temporarily making it hard to get decent pics. The OTG components come out next week which is why the small equipment room is a mess. Grid power is this week, the grid tie secondary final attachments are next week. My solution will need to happen after next week since I won’t have 24 volt power to the pumps anymore. I’ve made some inquiries with some contractors. Nothing yet.
     
  11. Dana

    Dana In the trades

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    Location:
    01609
    This type of boiler is most efficient when operating at minimum fire. As long as it isn't short cycling (=burn times << 3 minutes with more than 5 burns per hour) and the room temperatures aren't overshooting the thermostat setpoints it isn't burning any more propane than necessary to heat the house. A buffer tank or thermally massive hydraulic separator isn't going to change that- spending the buffer tank money on a round of blower-door & infra-red camera directed air sealing & spot insulation would be a better investment in comfort and efficiency.

    Alternatively/additionally, controlling the boiler with floor thermostats and spending the real money on a cold climate ductless mini-split or two to manage the room temperatures would in most cases be dramatically cheaper than heating with condensing propane, now that you're going on-grid, and it would give you extremely high efficiency air conditioning in summer too.


    If you're not reconfiguring the system the cheapest/easiest thing to do would be to plumb in one of the lower power "smart" pumps yourself, controlled by a 2-zone controller, assuming you have those skills. As a DIY it could run about $600. (~$200 per smart pump plus another $50 flanges/fittings plus ~$150 for a 2 zone Taco SR502-4 or similar zone controller and some wire.)

    Yet another pump that could work for you is the AquaMotion AM55 running at the lower variable speed or fixed speed. The pump curves are on page 3. These can be had through the big orange box store for under $200/each.
     
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