In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Please critique this design
I'm not sure if I've seen this exact design anywhere, but it contains many of the concepts that I learned about on this website and others. The cartoon is below. Here are the system specs:
* Design day heat load 40k BTU/hr (@ 15F outdoor).
* Lochinvar Knight WHN-055
* primary-secondary with closely-spaced tees
* Turbomax 23 reverse-indirect DHW piped as a series buffer in the boiler (secondary) loop, on the boiler supply
* Thermostatic mixing valve for DHW (115F setpoint)
* System (primary) loop has a Grundfos Alpha in delta-P mode, probably running @ 14 gpm when all three TRVs are open
* Each of the three 50-ft baseboard runs will be "zoned" with TRVs, one on each run
* A single indoor-reset thermostat will be set a few degrees above target, used as a high-temp cutoff (i.e. ODR will be the main feedback)
* The boiler pump will be controlled by the boiler (0-10V signal) for constant 35F delta T, probably running between 0.5 and 2.5 gpm
* The boiler will control its supply temperature with outdoor reset (160F on design day, minimum 145F)
* The boiler will sense the Turbomax temperature and treat it as a zone, calling when the tank temperature drops below 145F
* The boiler will disable the system pump whenever the DHW zone calls
* I didn't draw the air separator and Y-strainer, but they will be included
* (side note: there will be a drain water heat recovery system)
I think the advantages of this design are:
* No short cycling, even with 50ft fin tube zones at 110F
* Return temperatures will vary between 110F and 126F (design day), so the boiler will condense most of the season and maybe beat 90% efficiency on design day
* Even heating within a zone: Design day baseboard temperature of 134F has 8F delta T
* Primary/secondary piping satisfies Lochinvar's recommendation
* Only 2 pumps needed
* No expensive controls beyond what's included with the boiler (unless you count the built-in controls on the pumps)
* (un)availability of small, inexpensive, efficient circulators with 0-10V control?
So, what do you all think? Glitch, fix, or something else? Please critique. Note that this is for a retrofit, so the baseboard is a design constant (obviously radiant would be preferable).