Now that my wife and I are involved in BPI training and plan to conduct field test at our residence, the work scope for integrated HVAC has become more involved. We'd like to use our efficient tankless boiler AND have old style equipment remain functional for use as a BPI field test site.
We're looking for an HVAC installer who has thoroughly mastered combined heating w/ air/water option.
I have also posted at Heating Help dot com > search Therm_lag (me) and scroll to Integrated HVAC.
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 (see attached "Pic"). 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 (see attached load estmate from metered use).
The coil placement should allow for a customary filter rack at the horizontal run of return next to the furnace (see attached "System"). 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.
When conducting BPI testing, combustion safety test is performed by the test candidate on both a standard tank DHW heater and on the furnace. 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 valve 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.
We're interested in additional efficiency options that I'll open at existing or other threads:
Zoned comfort control,
Central AC with high efficiency equipment
Intentional ventilation, based on CO2 content of indoor air
Circulate ground-tempered water for sensible cooling
Well, 2 yrs later (though none the wiser!) system now functioning captures most of the intent of concept described above. See photo identifying the set-up I'm monitoring (hurry!) mid-Nov to early Jan, before numerous insulation defects are corrected. This HVAC approach MAY be the least costly path to 95% efficient Home and DHW heating for the majority of US single-unit housing. I'm out a bit more than $7,500.