New York Sanity check on system design

Discussion in 'General Discussions' started by Jderm, Apr 19, 2022.

  1. Jderm

    Jderm New Member


    I have learned a great deal on this forum over the past few months. I was wondering if anyone could provide a quick sanity check.

    I have been working with dandelion energy, a GSHP installer in NY, CT, and NJ. They have designed a system for my new construction home (4600 sq feet conditioned space) that sounds fine. The home is about 45 minutes north of Albany, NY.

    The Manual J for the home has a winter design load of 66,000 BTU/Hr. The basement, 1st floor, and second floor, have heat loads of 18000, 30000, and 18000 BTU/hr respectively.

    They have proposed a four-ton ENERTECH HP (I think this is also geocomfort?) that is zoned for the basement and 2nd story. A three-ton unit will service the 1st floor. These units should be able to output a total of 28200+22700=50900 BTU/hr at EWT=30F. Based on these figures, the balance point for both units should be around 5-10 F.

    I may be overthinking things, but one concern of mine is that the zoned system (basement + 2) will behave oddly during the fall and spring. Although the unit seems appropriately sized when both zones are calling, a single zone (with a winter design load of 18000 BTU/hr) will receive the 1st stage capacity of 33100 BTU/hr (brochure specifications at EWT=50). Does this seem oversized for heating?

    For cooling in the summer, the situation will be even worse, as the first stage cooling of the four ton unit is 38,000 BTU/hr. According to the manual J, The basement and 2nd story each have cooling loads of about 11,000 BTU/Hr. Is this so grossly oversized for cooling that I should be concerned?

    There is a water furnace dealer in the area but their quote was much higher and their financing options more limited, so I do not think I can afford 5 ton series 7, which would remove and concerns for over sizing.

    Thanks for reading.
  2. xSpecBx

    xSpecBx Member

    I’m no expert and I’m sure some smarter people will chime in if I’m wrong, but I don’t think the system design is necessarily a problem, as long as each floor is in a separate zone with and independent thermostat and zoning dampers in the ducts. In this case, the heat pump will only service the necessary zone. If you’re basement and 2nd floor are just one zone, than I could see having issues maintaining temperatures.

    Assuming independent zones, the stage 1 size does not necessarily matter. During warmer periods, the heat pump will just short cycle a bit, but you still want to be designed so that stage 2 can handle for both zones calling at once. I would assume they would have the system run in stage 1 primarily, regardless of number of zone calling, unless the heat loss requires stage 2.

    I have a single 4 ton hydron module (enertech is the parent company) servicing 3000 sq ft. 600 in the basement, 1600 on the first floor and 800 on the second floor. I have 2 zones, one for the first floor and one for the second, with the basement on the first floor ductwork. I will note that my basement does get colder in the winter than the thermostat set point. This is mostly due to my hybrid hot water heater being down there and it removing warm air and blowing cold air into the basement to make hot water, but there is also no dedicated zone there, so there is nothing actively trying to maintain the correct temperature. If yours is going to be setup a similar manner without a dedicated zone, you may have a hard time maintain the same temperature as the rest of your home as the basement temperature will be dependant on the 2nd floor thermostat temperature.

    The heat loss for my house was roughly 38,000 btuh with stage 1 putting out 32,000 btuh and stage 2 at 39,900 btuh. When it’s warm out, like right now, my system will short cycle when either zone calls for heat. System was designed to maintain an inside temperature of 70 degrees to an outside temperature of 8 degrees. Located in southeastern CT. You can take a look at my monitor on www dot welserver dot com /WEL1091 to see how it runs for yourself.
    Last edited: Apr 21, 2022
  3. SShaw

    SShaw Active Member Forum Leader

    A 7 Series with three zones seems like a better fit, since it can modulate capacities and airflow to better meet those loads. I have a zoned 4T 7 Series serving two zones, one 45K and the other 10K, and it works OK. Zoning does dumb-down the variable nature somewhat, limiting the number of speeds used.

    One of the bigger issues with zoning equipment is managing airflow and the duct design. If the basement is the only zone calling, your unit will try to push airflow for 33,100 BTU through the basement ducts, so the ductwork would need to be designed correctly to handle that. Waterfurnace has design guidelines and design software for zoning, so hopefully your designer/installer would use those.

    Also, the Manual J figures are maximums based on the hottest/coldest 1% days, so the issue could be more pronounced 99% of the time.
    Deuce likes this.
  4. Jderm

    Jderm New Member

    Thank you both for your comments. I would definitely prefer the series 7 for the variable compressor stages and simpler duct layout. Also I feel that a single unit servicing the entire house would be economical in the long run. Two units, double the trouble.
    Deuce likes this.

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