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Thread: sizing a new gas boiler and indirect water heater

  1. #31
    In the trades Dana's Avatar
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    Basement cooling loads are a tiny fraction of the cooling of the upper floors, since they typically have limited window area, and ~75F conditioned space above it rather than a 130F attic. But if you DO put a single-head mini-split in the basement, the 3/4 ton Daikin Quaternity is probably the best choice, since it has independently settable relative humidity & temperature setpoints, and can dehumidify in either heating or cooling mode (without any sensible heating or cooling if the temperature setpoint has already been met.) It's considerably more expensive than a standard name-brand 3/4 mini-split, but since the primary cooling load of the basement is latent-load, it's the right mini-split for the load.

    A ceiling or mini-ducted cassette or two on the main floor could probably work out fairly well for both heating and cooling if you wanted to. A single mini-ducted cassette with split output in the top of the closet could probably serve both the office and bedroom. The big open dining/living room area could be served with a ceiling cassette. But that's a bigger investment than a cheap minimum efficiency no-name 1-ton with a wall-wart blob. A small 1.5-2-ton ducted split system would likely be the cheaper option for cooling-only, and would be small enough to provide reasonable latent cooling comfort (which is likely to be at least half your average load.) Like heating systems, most cooling systems are way oversized in the northeast, and while there's less of an efficiency hit to oversized air conditioning, you pay a penalty in humidity-comfort with oversizing. Mini-splits modulate with the load, and will usually provide higher comfort (and lower noise.)

    Most raised ranches have a gross thermal bridge and air leak point at the cantilevered overhangs. Dense-packing that with cellulose or a full cavity fill of open cell foam on those overhangs can help both aspects a lot. If there is room to add 2" of rigid EPS as a thermal break (EPS only, lest you create a moisture trap) for the cantilevered joists that's worth it in the long term, but not the highest priority. Stopping the air leakage at the cantilever is far more important- many were (wrongly) built with a ventilation gap between the sub-floor and batts (if insulated at all), and have no real air-barrier where the joist-bays cross the foundation.

    A hydraulic separator would make for an awfully expensive junk filter if it's not really needed from a flow-isolation point of view. The primary purpose for hydraulic separation is to be able to set the radiation flows and boiler flows separately. The radiation in the system design will have a range of flows at which it will work well, the boiler has a hard minimum flow, but also a max delta-T at which it can be operated, and over pumping the boiler leads to erosion on the internal plumbing. It's not uncommon to find a satisfactory flow rate at which both are happy, but this is best left up to a competent hydronic designer who will stand behind the design rather than a taking web-forum napkin-math stab at playing Jr. Hydronic Engineer.

    You don't necessarily need a $400 system component for the hydraulic separator though- when the flow requirements are modest it's possible to cobble up an acceptable hydraulic separator out of 2"-3" fittings with reducing tees- there's no real magic to it (but you still need to do the math.)

    BTW: While our average winter temps are more severe in central MA than the interior northern NJ, the design temps are not dramatically different. My 99% design temp is +5F, only 5F cooler than the +10F 99% design temp for Patterson or New Brunswick, whereas the binned hourly average winter temps are about 8-10F cooler.

  2. #32
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    It is a three day course, but you can do the math if the manufacturer will let you. It is certainly much easier to add a pump and go home...well, add a couple hours and a couple hundred dollars and a couple thousand in operating costs for the redundant pump..if it doesn't fail before it wears out, in which case you will have proved the probability of doubling the chance of a pump failure, since your beloved P/S system will not run without at least two pumps!

    P/S is not religion.

  3. #33
    DIY Junior Member cyruspinkney's Avatar
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    @Dana

    But if you DO put a single-head mini-split in the basement, the 3/4 ton Daikin Quaternity is probably the best choice, since it has independently settable relative humidity & temperature setpoints, and can dehumidify in either heating or cooling mode (without any sensible heating or cooling if the temperature setpoint has already been met.)
    Thanks for the suggestion. Humidity is already an issue down there, so I think I will look into that model, regardless of the price.

    A hydraulic separator would make for an awfully expensive junk filter if it's not really needed from a flow-isolation point of view...A hydraulic separator would make for an awfully expensive junk filter if it's not really needed from a flow-isolation point of view.
    Well it's apparent that I got some bad information, as it was explained to me the sole purpose for the hydraulic separator was to be a filter, with no mention of it's true purpose. I think I'll avoid that and go with the reducing tee setup if necessary.

    I guess I'm going to have to reach out to some of our contacts from the office and see if we don't have a competent hydronic engineer we can dial up

    @BadgerBoilerMN

    It is a three day course, but you can do the math if the manufacturer will let you...since your beloved P/S system will not run without at least two pumps! P/S is not religion.
    Once again, I'm not sure if your'e directing this at me specifically or you're just making general points. I don't recall claiming anything about P/S rather just questioning if that is a possible setup for my condition. What I am trying to do, however, is further educate myself on some of the finer points of hydronics for both my personal gain and my occupational benefit. I was under the impression that this forum was to share our experiences and help one another. If you were not directing it at me, I apologize, and let's just chalk it up to the lack of emotional clarity via the interwebs.

    If no one is comfortable taking a stab at helping me size the system, I totally understand, it's not your responsibility, I was just putting it out there. However, is there any other resource I can find online that I might be able to help me in my quest? I have no problem hiring someone to do the calcs, but feel it may be something I can look into myself. My architecture licensing doesn't involve this type of engineering (at least at this extent), but I do think i might enjoy checking the math out for my own peace of mind. This is not to say an experienced engineer wouldn't have better and more accurate information, but a little insight into that world is something I am interested myself.

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