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Is there any way to do this properly?

Mike_SheppardMike_Sheppard Posts: 575Member
I have inherited a problem system. Lost a bid to a low bidder now they want me to fix their install.

Two condensing boilers (oversized) 550kbtu each.

It’s a water source heat pump system. So the closed loop operates at 70 degrees. Sounds like a great application for condensing boilers. But then there is a single large make-up air coil that requires higher temperature water during the winter.

The boilers have to be installed primary/secondary to the water source loop. But then there’s the high temp make up air coil.

Old boilers were non-condensing, primary secondary with 3-way tempering valve for return temp. Make up air was piped secondary to the primary loop with it’s own 3-way valve control by discharge air temp (70 degrees). It didn’t work well before. Now it’s way worse.

I can’t think of any proper ways of piping this.
Never stop learning.

Comments

  • Larry WeingartenLarry Weingarten Posts: 1,553Member
    Hi, This sounds like one of those physics vs politics questions. You shouldn't have to turn into a pretzel to "fix" a poorly thought out system. Your original design was likely the right thing for the client. How about proposing to them, replacing what they have with what you originally designed? I wouldn't expect to see any smiles in the place until they experience your system doing what it should. :#

    Yours, Larry
  • Mike_SheppardMike_Sheppard Posts: 575Member
    @Larry Weingarten i agree. I’d love to tell them that. I figured I’d give this a shot. This is one of over 30 properties for this customer. We get a lot of work from them. If I can’t find a good solution then I will not propose one to them.

    Everything else is wrong too. The controls are all wrong. The venting is very wrong. It’s terrible.
    Never stop learning.
  • ratioratio Posts: 2,073Member
    Can they be separated, & dedicate one boiler to the loop & one to the make up air unit?
    Also, another vote to give them a price to tear it out & sell them what they need.
  • Mike_SheppardMike_Sheppard Posts: 575Member
    @ratio that is what I wanted to do. But not with a 550,000 btu boiler that would be extremely oversized.

    What will probably happen is I will tell them what the problems are and how to do it right and they’ll have the original installer come back to do it.
    Never stop learning.
  • Mike_SheppardMike_Sheppard Posts: 575Member
    Here’s a rough picture of what I am thinking. Won’t solve short cycling under light load. But I could program the condenser loop valve to have a minimum open position maybe. And also give it a larger operating range. Instead of 68 degrees on and 70 off, I could do something like 68 on and 80 off to stop short cycling. Not efficient but I don’t see this setup being efficient at all anyways.

    Primary boiler loop with heat injection secondary for condenser loop and another secondary for the make up air coil. Kinda like a duel temperature setup. I’m sure I drew something wrong here, just trying to get some thoughts on paper.
    Never stop learning.
  • ScottSecorScottSecor Posts: 280Member
    @Mike_Sheppard we almost never see heat pumps here, so I won't comment on that aspect.

    However, if there is any way you can salvage those almost new condensing boiler without bashing the installers you will likely earn a lot of trust and a customer for life. Just a wild idea, could you treat the high temperature loop like a indirect water heater? Make it a priority zone, regardless of outdoor temperature?
  • John RuhnkeJohn Ruhnke Posts: 871Member
    edited October 8
    Mike,

    This is actually good news!! My guess is the guy who called you out to look at the problems actually wanted to hire you in the first place. But somebody in accounting wanted to save money and now its all screwed up.

    If you solve these problems and get something workable they will be willing to stick with you in the future at a higher price on other projects.

    Write up a rough note report that explains why your design is better. Then list your recommended changes and related charges to get the existing system workable. Then verbally throw some options and rough numbers at them while explaining price differences, short falls and solutions. Tell them these prices only cover visible problems. Unforeseen problems are extra. This is to get a workable system. A optimal system would have to be done by scratch. Of course the optimal system is better and then tell them why. But you are willing to work with what is there.

    After some back and forth and once you get an idea of how far they want to go to fix things then draw up a final quote. Again list unforeseen problems will be extra and hand it in.

    Don't try to charge too much because you don't want to rub there nose in it. But do charge enough so they regret going with the other guy.
    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • John RuhnkeJohn Ruhnke Posts: 871Member
    edited October 8
    You need an opening line.

    "I am willing to do you a favor. this time only, because we are friends and you are a real valuable client. For anyone else I would have left 10 minutes ago."

    You want to put some future placed fear in this situation. This way they will be afraid to hire the low bidder on future projects but apreciate the fact that you bailed them out.
    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • Mike_SheppardMike_Sheppard Posts: 575Member
    > @ScottSecor said:
    > @Mike_Sheppard we almost never see heat pumps here, so I won't comment on that aspect.
    >
    > However, if there is any way you can salvage those almost new condensing boiler without bashing the installers you will likely earn a lot of trust and a customer for life. Just a wild idea, could you treat the high temperature loop like a indirect water heater? Make it a priority zone, regardless of outdoor temperature?

    @ScottSecor i thought about that, but it is a constant load. It runs 24 hours a day supplying make-up air to the building. So it would have to have some amount of heat running through the coil at all times. It had 180 degrees running through it today and was discharging 130 degree air. It is supposed to be discharging 70 degree air. Hopefully it won’t require a full 180 degrees but who knows once it gets cold outside.
    Never stop learning.
  • Mike_SheppardMike_Sheppard Posts: 575Member
    @John Ruhnke i like they way you think!

    Sadly the boilers are literally only a week old. They were just started up last week. The whole thing is a mess. This customer is extremely cheap and this is no where near the first time they’ve selected this same company over us. I won’t name the company but it’s an internet company who just subcontracts to local contractors to get the job done. They consistently come in at half the price of everyone else but the job is completely wrong every time. It is frustrating.

    I think I could make this sort of work with what they got if they’re willing to do a complete piping and controls change. Which at that point they might as well just go with a whole new system.

    I have no idea how this will turn out. I just need to come up with a bandaid fix for what they have now. If they don’t want to do it I guess they can limp what they have along until the new boilers are ruined in a couple of years.
    Never stop learning.
  • ScottSecorScottSecor Posts: 280Member
    Maybe put a sensor on the discharge air and tell the boiler it's a dhw tank and you want 70 degree air (dhw)????
  • Mike_SheppardMike_Sheppard Posts: 575Member
    edited October 8
    Hmm that could be interesting. Never tried that before. Depends on how adjustable the modulation settings or PID is on the boiler.
    Never stop learning.
  • John RuhnkeJohn Ruhnke Posts: 871Member
    @Mike_Sheppard,

    Is this the first time they asked you to look at a system that they screwd up?

    You need a conversation with the hiring maneger. You need to explain to him that this is no way to do business. fuel savings alone will make up any cost differences. Using a condensing boiler to make 180 water 24/7 is going to run up a astronimical bill. Calculate that out for a whole yesr. Do the math. Running a boiler at 70 or 80 degrees to heat up the heat pump loop is like 300% cheaper then running the boiler at 180 and then knocking it down after to 80. Then figure repair bills on a problem system are an extra added expense and reacure more often. He will spend more money yearly on repairs and fuel that in a short period of time will cause the low bidder to end up more expensive.

    Set him straight. Tell him you wont bail him out in the future if he continues to do work with these butchers.
    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • Dan FoleyDan Foley Posts: 1,180Member
    Mike,

    We work on many buildings with building loops and water source heat pumps. I have an idea but a few questions first. Give me a call tomorrow to discuss.

    - DF
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,962Member
    What am I missing? Why can't you put a mixing valve on the heat pump loop with a controller to maintain the HP loop at 70 deg. Then just run the boilers at the temperature the make up air requires.

    Also, because it's a MU air unit I would pipe it so you have constant circulation through the coil to minimize freezing

    The HP loop needs constant circ as well so they don't trip on lack of condenser water flow.

    It will probably take more pumps and some engineering to do this but it certainley can be done
  • Mike_SheppardMike_Sheppard Posts: 575Member
    edited October 9
    @EBEBRATT-Ed the water source loop is constant circulation.

    There was a 3-way valve for the water source loop but the installers removed it and replaced it with a 2-way valve. The 3 way will be going back in.

    The MUA unit is what I’m trying to fit in here correctly without causing too many issues with the boilers cycling etc. I like the idea of just running the boilers at the temp the MUA unit needs. That could eliminate its 3-way valve.

    That would require modulating the boilers based on the MUA discharge temp. I need to figure out if that is possible with these boilers.

    EDIT: So they do have an option for a 0-10v input to reset the target temperature. I could use a control like a T775 to control the boiler setpoint via MUA unit discharge temp, as well as the 3-way valve for water source loop temp.
    Never stop learning.
  • John RuhnkeJohn Ruhnke Posts: 871Member
    edited October 9
    Idea 1) This is the better idea.I think one boiler should be dedicated to the heat pump loop if it is big enough to handle the load. Running that boiler at 70 to 80 degrees will be real efficient and really cut the fuel bills down. The other boiler do the make up air. A buffer tank for the mu to cut down short cycles.

    Idea 2) If you need two boilers for the heat pump loop, I would try a control strategy with a storage tank. Run the boiler inefficiently at higher temp to heat up the storage tank. Give the storage tank priority dedicating high temp water to tank only. After tank is up to temp its zone shuts off and the the heat pump loop pump activates and sends 70 water to the boiler and runs at 70 degrees. Storage tank would then have a pump and supply higher temp water to mu coil.

    When this is all over you will save your client a huge fortune in fuel bills. Those old boilers running the heat pump loop vrs the mod/con will seem unreal!! The gas company will send someone over to change the meter. Get the client excited about this!!
    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • Larry WeingartenLarry Weingarten Posts: 1,553Member
    Hi, As they have lots of properties, could the boilers and possibly other equipment be stored for future use in a different building by the client? That could reduce the sting of the bad job they bought.

    Yours, Larry
  • ZmanZman Posts: 5,062Member
    The boilers should run on the appropriate reset curve for the MAU's. They can then supplement the heat pump circuit as needed with mixing as you illustrated. The controls for the heat pump side will be interesting. Siggy just put this out which might give you some ideas https://www.pmmag.com/articles/102414-modern-hydronics-done-right-volume-4

    Don't forget to call Dan Foley :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • John RuhnkeJohn Ruhnke Posts: 871Member
    edited October 9
    The load of the MAU's has got to be very small as compared to the heat pump load. Less than 5%. 70 to 80 degree temps are real energy efficient. The MAU's are a constant 24/7 load at a higher water temp.

    The goal is to run the boilers at 70 to 80 degrees the majority of the time. Constantly bringing the temperature up because of a small load is going to kill the efficiency. So the storage tank allows the boiler to be in high temp mode for a shorter deration of time. 120 -70 is 50 degree delta tee water temperature. This is a big difference in efficiency for a condensing boiler. When in condensing mode the increase in efficiency as the temperature drops doubles. According to the chart below the efficiency in 120 degree temp runs at 87% efficient and at 70 degrees it jumps to 98% efficient. Its a huge jump!!






    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • John RuhnkeJohn Ruhnke Posts: 871Member
    edited October 9
    According to this Durkin Study which I find to be very accurate. Also backed up by another more in depth euro study.

    On a standard conventional old outdated boiler to mod/con conversion with odr you get a 50% average fuel savings. I think with the set up above running 85% of the time at 70 to 80 degrees you will get that to a fuel savings of 60% average!!


    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
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