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Integrated HVAC

Therm_lagTherm_lag Member Posts: 30
Looking for posts related to system I'm installing - pls direct if I've overlooked.  I am installing an integrated HVAC system in my modest residence:

1. Install 95+ efficient tankless combined heating boiler (ModCon, sealed combustion) to supply DHW and hydro-coil (air handler unit or AHU) replacing 70AFUE FA (60k load), 0.55EF tank water heater, and 2.5T R22 AC w/ new type, retaining most piping and duct work.

2. Control flow from AHU, perhaps trimmed to supply pressure, to achieve variable flow (see #4) and to reduce fan energy.

3. Connect AHU to filtered outdoor air, controlled to limit interior


4. Zone dampers at air terminals to direct conditioned & fresh air supply only to occupied room(s).

5. AHU to accommodate AC coil, and zone control will be modified to maintain adequate air flow across coil.

Installers seem to have difficulty selecting an AHU w/ variable flow based on duct pressure, and accommodating a water/air heating coil.

I plan to install Navien CH unit to re-establish DHW (failed tank), though have not yet found AHU that will perform per above.  Comments welcome.  I can document system as it is installed. 

I'm an energy auditor (finally making some change after 34 yrs) & intend this system to prototype what might be installed in any house having outdated FA, tank heater & AC, while working with existing piping & duct work.


  • SteamheadSteamhead Member Posts: 11,378

    do you plan to vent that mod-con? If you can't do so above the snow line, and satisfy other Code requirements, you could be asking for trouble.

    At first glance the strategy sounds reasonable, but there's at least one "gotcha"..........
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • ChrisChris Member Posts: 3,056

    I'm sorry but a Navien is not a boiler. Does not have a rating as a boiler and is a water heater. That's why they call is "heating box". In some municiplaties you cannot install a water heater as the main source to heat. The rating of the Navien is not based on AFUE as a boiler is. So as an energy auditor the use of a water heater isn't the best road to travel on.

    Find a true mod/con boiler, use an indirect for the hot water and let the boiler rip on outdoor reset. What was the heat loss? You never posted that. We all know that hydro air is sized for the cooling load and that the air handler is most likely oversized. Could start your heating curve at 160 and work down from there.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Bob BonaBob Bona Member Posts: 2,081
    edited October 2010
    I'm thinking

    maybe wait a month or two. Trane/American Standard is starting to ship their new air handler with integrated HW coil. Not sure if it's coming VS, but heard it has all controls included for hydro interface. Cabinet is supposed to be some sort of composite for lightweight. About time. If it does come VS, we got some sweet stuff there. First Co. has already a VS hydro A/H, but,'s ok..

    So, 1) Yes, mod con. No Navien for space heating. 2) Acheive this with VS air handler. 3) ERV/HRV 4) Trane Integrated Zoning System or Carrier Infinity System. 5) Up to now, the quality VS A/H's I know of have to have a HW coil bolted on. This may change soon. (see above).
  • IronmanIronman Member Posts: 3,535
    edited October 2010
    The Navien "CH""

    Is a new model that has a separate heat ex. and pump for space heating with dual set point controls. Not as heavy duty as a mod/con and indirect, but not as heavy in price either. You get what you pay for.

    ADP has a nice v/s hydronic AHU. Better than First Company's.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • HDEHDE Member Posts: 142
    Pay attention

    Your confused heating box is an actual product with no burner inside
  • Therm_lagTherm_lag Member Posts: 30
    edited November 2010
    So far . . . ready for AHU

    Navien installed.  We'd prefer having 95% or better efficiency, and not sure why combi boiler functionality takes the tankless efficiency of 98% (thermal) to 91 AFUE (we have model 180).  See 

    Pic of unit attached.  

    Suggestions of AHU having heating coil and VS are helpful and appreciated:

    ADP  --


    Thermo Products -

    Perhaps tightening the house and supplying air at ventilation standard (see attached) has little cost premium compared to AHU.

  • Therm_lagTherm_lag Member Posts: 30
    edited October 2010
    Picture of Boiler & Description of System

    Installer is still searching for VS air handler that has water coil built in.  We're looking for 2 ton capacity as current 2.5 ton AC does not run full time at most severe heating conditions.

    People like to see system description as shown.
  • tim smithtim smith Member Posts: 2,226
    Re; Delta P air handler

    I think Titus makes one but I am not sure they make one in vertical config. What I have done is buy a good quality standard air handler with water coil, replace fan motor with 3 phase direct drive motor and install a variable freq. drive, maybe honewell smart drive along with delta P transducer. 0-10 vdc.  I put multiple zone dampers and and set my drive to maintain .3 esp. It is pretty cool to watch the vfd modulate the fan speed as zones open and close along with of course boiler is mod con that sees a lower delta t with lower air flow so then boiler mods down at same time. Pretty cool. Tim
  • tim smithtim smith Member Posts: 2,226
    Re; Delta P air handler

    I think Titus makes one but I am not sure they make one in vertical config. What I have done is buy a good quality standard air handler with water coil, replace fan motor with 3 phase direct drive motor and install a variable freq. drive, maybe honewell smart drive along with delta P transducer. 0-10 vdc.  I put multiple zone dampers and and set my drive to maintain .3 esp. It is pretty cool to watch the vfd modulate the fan speed as zones open and close along with of course boiler is mod con that sees a lower delta t with lower air flow so then boiler mods down at same time. Pretty cool. Tim
  • Therm_lagTherm_lag Member Posts: 30
    edited October 2012
    Two Years Later - ReStart

    Our experience over past two years is to have installer come and take a look and then try to sell $$$$ packaged products that take us in an entirely different and inappropriate direction.  Our shower produces 3/4 g/min mist,  dishwasher is high eff, & there's 2 (count them, 2) ppl -- we really don't need a 60g storage tank!!  We're both full-time energy auditors - not advocates of "deluge" shower!

    We don't mind spending $$$ for expert services and believe one can achieve great efficiency with $$ products that are not a packaged commercial offering.

    We take our failure to connect with an installer who has mastered combined water/air heating a blessing as we're now BPI test proctors and want to have combined heating AND retain our natural draft furnace.  In addition to retaining our decrepit furnace we'll install a natural draft tank water heater to let candidates for BPI certification perform a complete equipment safety test on actual old and inefficient equipment.  (Why a homeowner would not replace old  inefficient equipment prone to hazard beats me, but that's another issue.)

    Following is the revised system description that integrates heating & DHW AND integrates functioning old inefficient equipment that will be available when we proctor BPI field tests.  Per initial post please direct me to other HH threads that may address specific questions (to avoid redundundancy) and I will report back on any elegant products and practices as we progress.  I'll also track progress at where my wife and I place other info.  We have one Chicago-area installer who seems interested, and we'd welcome another.

    Combined Heating System with

    Retrofit of Existing Furnace for Air Circulation

    Use existing furnace which will remain connected and functional for use to conduct BPI equipment safety testing

    Place hot water coil (“hydrocoil”) to receive heat from tankless boiler (Navien CH-180) that now provides only hot water.  Possible coil locations:  at opening to blower compartment or at supply plenum outlet or supply trunk, or other location.  Heat loss from the trend of gas use to temperature indicates required peak heating capacity of 33,000 BTUh. 

    The coil placement should allow for a customary filter rack at the horizontal run of return next to the furnace.  We assume filter will be ahead of coil if coil is placed at return.

    Install variable speed fan motor in place of existing, brushless or ECM type.

    Wire fan for set speed when furnace is operated, using existing “round” room thermostat.  This fan mode will be used when we conduct BPI field test.  It is acceptable to wire fan for fixed speed for air conditioning (see below), also using existing room thermostat. 

    Install outdoor reset thermostat sensor that activates tankless boiler temperature modulation.  The sensor should be a standard accessory for the tankless boiler.  Sensor may have been supplied with tankless boiler or it may require purchase. 

    Install pump between tankless boiler and coil.  Advise about pump control, variable speed, how to activate pump on call for heating but not on cooling.

    The furnace blower control: when furnace is operated to circulate heat from hydrocoil, vary from low speed when heating load is small and water from hydrocoil is least hot, to a higher speed sufficient to pull 33,000 BTUh from the coil when the set maximum temperature from the tankless boiler is called.  To realize high efficiency heating, keep tankless boiler in condensing mode and operating at the lowest temperature that can provide comfort.  It is desired to have long blower “on” time to enhance air mixing, also consistent with maintaining circulated air temperature at a relatively low temperature difference.

    The tankless boiler control provides for scheduled temperature setback and

    we anticipate using the programming features of this thermostat. 

    (See load derived from actual gas use and temperature below - also "graphical load calculation" post)

    When old equipment is operated during BPI testing, the candidate will perform combustion safety test of both a standard tank DHW heater and on the furnace (see attached pics).  We will maintain the vent and chimney for this purpose (the furnace is natural draft design).   We plan to have a natural draft tank water heater installed to allow testing of the two appliances that may be found in older residences.   Installation of a tank water heater, connected to the existing vent “T” and gas pipe, may be included with this work.  An older functioning 30g water heater is preferred.  Rather than pipe into house hot water supply this installation should include a “water use” pipe that is installed to a hot water tap at the near-by laundry sink.

    When using the existing furnace gas burner when conducting a BPI test,

    we will shut off tankless boiler operation.  Perhaps “pulling the plug” from tankless

    boiler will be OK, since the appliance is designed to retain settings during power outage.  Keeping the existing furnace electric circuit intact, and separate from wiring for the boiler may require thought, especially how the blower is energized.

    Other Efficiency Work for Future

    We are interested in zoned comfort control, able to control air supply separately to the basement, rear bedroom , balance of 1st floor, and perhaps the 3-season porch and perhaps an attic expansion space.   Zoned control will probably be done at a

    later date, although the design of system should accompany zoned control.   Trim blower speed based on pressure in supply duct?

    We'd like to re-establish central AC with high efficiency equipment.  We suppose that  1.5 ton capacity is sufficient (2 ton max) operated so as to maximize dehumidification.  ( We've been OK except for a couple of days the past two summers w/ one 7kBTU window unit).

    We'd like to install intentional ventilation, with a ducted connection between air handler and outdoors with control to provide outdoor air based on CO2 content of indoor air.  With zoning (see above), we suppose this will maintain a minimum fresh air setting in areas that are occupied.  Comment:  with one sensor at the return, this may require bringing furnace blower on for a few moments on a schedule to “sense” CO2 at times when heating or AC are off.  Perhaps not if the fan control maintains

    operation for long cycles, and given occupant behavior to open windows in when

    heating/cooling are not required. 

    It is desired at a later time to circulate ground-tempered water for sensible

    cooling, to meet some of cooling load, in summer, and coil fittings should be accessible for this later installation.

    I hope this is helpful for "wallies" who need a write-up of particular installation work.
  • TechmanTechman Member Posts: 2,144

    A couple of things to check out. Having the hot water coil before( return side) the AHU may not be good for the blower motor,possibly overheating the motor.And not all variable speed (ECM) motors are created the same,some can be used w/ zone dampers and some cannot be used w/ zone dampers.
  • HomeOwner1HomeOwner1 Member Posts: 134
    You are incorrect.

    It is a boiler. Please stop posting bad information. This is very frustrating to homeowners trying to research their options.
  • RJRJ Member Posts: 484

    You should think about installing a HRV ( heat recovery ) if your going all out in this proposed system
  • TonySTonyS Member Posts: 849
    What temp water

    are you running to your coil?
  • Therm_lagTherm_lag Member Posts: 30
    BIG discussion about HRVs

    Thank you for this comment!

    Martin Holliday's "Are HRV's Cost Effective" in Green Building Advisor provides interesting guidance.  Yes, I intend to provide outdoor air, though controlled by CO2 and delivered to zones that are occupied, and limit ventilation to times of occupancy. 

    I want to go "all out" in the sense that all items of equipment that I already have that can be incorporated into a 95/95 space/dhw set up I'll keep.  I'm going all out to explore the least cost means to achieve a 95/95 system in a large fraction of US housing. 

    With this objective I want to avoid cost of HRV if it is not justified.  We'll use exhaust fans at bath and kitchen.  By tightening house what are now house leaks to outdoor air supply terminals.   Consider with a balanced HRV I have left house (wind and stack) leakage unchanged.  HRVs may not be tolerant of large intermittent latent loads and airborne cooking stuff from these sources, so I'll need to have the bath/kitchen fans anywho.  

    BTW I continue to struggle with finding an HVAC installer who can work out the details of installation of this system.  Fortunately, I have had plenty to do on other projects since initiating the search 2.5 yrs ago.
  • TonySTonyS Member Posts: 849
    The reason I ask

    is because you are venting with pvc and even if you are using outdoor reset, if design conditions require water temps above 140 you must use sch80 cpvc or pp.

    Also your condensate line is a tripping hazard and would not pass code.
  • gennadygennady Member Posts: 680
    BPI and all this green thingis

    Unless price of gas and oil will go up dramatically there is no incentives to install efficient equipment. Amount of paperwork  and related expenses defeats the purpose of rebates. Clients who chose to go through these programs are from the bottom of the pot and generally just want to get systems installed free of charge, The real moving force today in high efficiency business are clients who enviromentally concerned, the ones who want the best equipment market has and oil customers who think gas will stay cheap forewer

    The reason Europe and the rest of the world is so ahead of US in energy efficiency is beacause they pay at least double of what we pay for oil and gas. they are forced to be efficient. We in US are forced to be unefficient.  This is the case when one green beats another green.
    Gennady Tsakh

    Absolute Mechanical Co. Inc.
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