Bastardized system of my own creation

brewdesign

As a quick intro, I've been looking around the site for a few weeks and this is my first post. A brief chronology of the last decade: purchased my first home, a 800 sq ft 2 bedroom ranch, in 2006 (not the best timing) built my first garage (2007) and designed my first small hydronic system (in floor garage heat). I have relied upon Siggy's Modern Hydronic Heating for design and found out a few things by trial and error along the way, but the garage system is works as designed, no complaints. The house is in Berkley, MI.

In 2008 I started planning house expansion which included more hydronic heating, specifically for a kitchen addition and second story bathrooms. I side vented the existing forced air furnace via approved Tjernlund kit and installed a power vent water heater in preparation of the second story addition for which I didn't want to design around and make compromises for a flue. The water heater is a 50 gal / 60 BTU unit with space heating ports.

By 2010 the 12x16 kitchen addition was framed and 1.5" concrete thin slab poured over 1/2 pex-al-pex at 12" oc. This is zone 1. Zone 2 covers the adjoining existing kitchen, 8x16, with nail up extruded heat exchanger plates, 9-12" oc. Entire kitchen area is tiled.

From 2012-2015 the remaining 32x37 second story addition was completed (yes 3 years of construction while living in house) the upper floor area which contains zone 3 (upstairs master bath and walk in closet) and zone 4 (kids bathroom). Both zone 3 and 4 are heat exchanger plates, same as zone 2.

The house is 2100 sq ft plus 700 sq ft basement.

These 4 hydronic zones are running off the water heater via a Taco XPB X-block and 4 port manifold. This works reasonably well with the water heater only cycling a few times an hour with no domestic hot water flowing and abundant domestic hot water available even during design load conditions. The system operates on outdoor reset control and uses no additional controls, runs until WWSD.

The 57k input 80% AFUE forced air furnace (with 2 ton a/c unit) now feeds both the existing 800 sq ft house (less existing kitchen area), existing basement, and the new upper floor 4 bedrooms. The heat load isn't that much since the upstairs bathrooms radiate heat out -- the system works decent for 3 of the 4 rooms. Room 4 floor is actually over outdoor porch, has R30 or so insulation under it and is under heated during design load conditions. I intend to add a 2k BTU low temp radiator running off the existing hydronic circuits on outdoor reset to address this.

The forced air furnace doesn't have zoning dampers for first or second floor and exhibits relatively poor airflow once it reaches the upstairs bedrooms. Ductwork consists of 6" rigid steel round duct, taped and R6 insulated from basement to upper bedroom. Bedroom 3 and 4 ducts run 20' in the attic before exiting from the ceiling near exterior wall/window. Bedroom 1 and 2 run under 2nd floor floor before exiting from the floor near exterior wall/window.

I don't yet know how poorly the A/C will function since last summer was very mild.

Currently, I have 2 Rinnai ABH045 ECM air handlers sitting in the garage and i'm shopping for a boiler and indirect water heater to replace the existing furnace and water heater. One air handler will supply the upstairs (with 1.5 ton a/c unit) and the other (with 1.5 ton a/c unit) will supply the main floor and basement.

This all sounded like a great idea until I began to drive myself crazy with boiler micro loading.

Since the hydronic system operates on full reset, the heating load could range from 2k-14k BTU. The whole house load via Manual J, to the best of my abilities, is 48-55K BTU, depending on variables such as air infiltration and basement heat loads. The hydronic load breakdown at 80F min through 130F design temp is Zone 1: 1400-8500, Zone 2: 450-2750, Zone 3: 300-1800, Zone 4: 200-1200.

I started looking at WM GV90+ boilers, pros being cast iron durability (except for o-rings only they use) and higher efficiency than conventional CI boilers (yet debatable whether you will run in condensing mode much). I also looked at the Slant/Fin Victory VSPH due to their fair price, direct venting, steel push nipples and good boiler control logic. The thought here was that the boiler will be firing full bore at way more than needed BTU output but has enough mass to run the micro loads for a longer period of time before re-firing. Of course when a DHW call is present or call from the hydronic air handler, it would operate continuously.

I've also looked at mod-cons with inputs in the 50-70k BTU range and turndown rations as high as 10:1 on slightly larger mod-cons. Bottom line is that the minimum BTU output is in the neighborhood of 10-30K BTU and it will still cycle off and on at lowest fire rate. I question at this point whether there is any real world advantage of using a mod-con during micro loading say 25% of the minimum fire rate. Adding a buffer tank to a mod-con seems pointless since this is typically a high thermal mass boiler bandaid.

I've looked at inside-out (whatever you call them) indirect water heaters but they require hundreds of thousands of BTUs to deliver acceptable DHW. Triangle makes a comfort water heater (for which I find zero literature except for a sales brochure) that is intended to double as a buffer tank, so it appears.

In regards to piping, the intention is to use primary/secondary piping with the indirect water heater and air handlers running off the secondary loop. Also running off the secondary loop would be an injection system (possibly reset control) feeding what I'll call (for lack of better term) loop 3 which is the hydronic radiant heat zones.

I'll stop at this point in my ramblings... the question at hand is what would you do and why. Tear it all out and put in baseboard heat and mini-splits? Stick with the hydronic air handler and then choose the mod-con or the high mass boiler and why? Use a pricey built in type of indirect system like a HTP?

Thanks in advance.

Ryan

Paul S_3

Why not use a lochnivar khn 85 (can modulate to 8k btus) with an indirect wired to take priority over the space heating...this should take care of your dhw load set tank to 150f and mix down plenty of hot water..i like an indirect over a standard water heater warranty is a lot longer usually lifetime for original purchaser....the dhw capacity and recovery is alot more than a standard wh....i would use a buffer tank sized for a minimum run time which will help with the micro zones ....the boiler may not even cycle in some cases....buffertank will also act as a hydraulic seperator.... (primary secondary piping)....since you are doing the work .....remove the forced air install baseboard or panel rads sized to meet your design day at a lower temp ....lets say 150f....mini splits for a/c.....this is what im doing in my home....your radiant zones can be mixed down with a injection setup, thermostatic or motorized mixing valve providing full outdoor reset to these zones using tstats just as hi limits.

Gordy

Question is the forced air having to pick up any of the heating load? Or is it there strictly for AC season?

You may want to combine some zones.

The UFT 80 or as stated the KHN 85 has the low end modulation, and btus to muster DHW.

brewdesign

Paul and Gordy, thanks for the suggestion of the other boilers. I had not researched those boilers and will do some more research.

Gordy, the forced air is necessary for heating also. The radiant zone BTU are not enough to satisfy the heating loads during design temperatures. The forced air typically runs when ambient temperatures are in the 40F range.

I've attached a drawing of what I'm currently thinking about doing. The drawing shows a conventional boiler but it would apply to a mod-con also.

I've searched around and have not seen anyone run a tank-in-tank indirect water heater in "reverse" but it seems that it could work. Essentially the DHW in the inner tank would transfer its heat back into the "heating water" in the outer tank, acting as a buffer. There would be a limit to how fast the transfer could occur... but I don't know how to calculate whether the transfer rate would exceed the radiant load of 14K BTU at design temperatures.

I'm sure I'm not the first to have thought of this... if anyone has suggestions please point me in the right direction.

Gordy

Turbo max. Give it a look.

SWEI

The SMART outer tank is plain carbon steel (not glass-lined.)

Gordy

I see you disagree with combining some zones. This is one way to help curb cycling. Micro loads while gives the user discrete control of a space needs to be well thought out, or unintended consequences arise. That is low load cycling of the appliance, which then needs a buffer to counter the effect.

brewdesign

SWEI said:

The SMART outer tank is plain carbon steel (not glass-lined.)

The reference I made to "reverse" was in regards to the action of pulling the DHW inner tank heat out though the heating water contained in the space between inner and outer tanks. I wasn't clear in my description but I think it is depicted better in the drawing.

brewdesign

Gordy said:

Turbo max. Give it a look.

I like the idea of the Turbo Max indirect heaters and the continuous DHW output rates are close to the Triangle Smart tanks but the 1st hour ratings suffer significantly if you compare with the larger Smart tanks. Of course I'm looking at worst case scenario such as a 90 gallon tub fill with the boiler cold starting.

The Turbo Max seems more appropriate with a 100+MBH boiler, I was trying to size the boiler closer to 50MBH so that it is size to the actual heating loads. I know there is an argument to size the boiler for DHW when the need is higher, possibly in this case.

brewdesign

Gordy said:

I see you disagree with combining some zones. This is one way to help curb cycling. Micro loads while gives the user discrete control of a space needs to be well thought out, or unintended consequences arise. That is low load cycling of the appliance, which then needs a buffer to counter the effect.

Which zones are you suggesting be combined? The radiant zones which are micro loads are all on/off together (4 radiant tube zones and one radiant low temp radiator). The only way to combine them would be to remove one fan coil and replace it with radiant baseboard heat or low temp radiators. Maybe that is what you are suggesting.

SWEI

In case you haven't seen it yet, the SMART Commercial Performance Data booklet has far more info than the brochure.

A bigger Turbomax will take care of the first hour problem, as would a separate DHW storage tank. With all that boiler side storage, do you actually need it?

hot_rod

what about a hydro-sep at the boiler. Gets you air, dirt, magnetic, and hydraulic separation for the entire system.

Pipe off the sep to the various loads. DHW/ buffer could be a secondary or parallel load.

Gordy

brewdesign said:

Gordy said:

I see you disagree with combining some zones. This is one way to help curb cycling. Micro loads while gives the user discrete control of a space needs to be well thought out, or unintended consequences arise. That is low load cycling of the appliance, which then needs a buffer to counter the effect.

Which zones are you suggesting be combined? The radiant zones which are micro loads are all on/off together (4 radiant tube zones and one radiant low temp radiator). The only way to combine them would be to remove one fan coil and replace it with radiant baseboard heat or low temp radiators. Maybe that is what you are suggesting.

Your prior post indicates 4 zones. Zones are seperatly controlled areas of temperature.

If they all come on at the same time then maybe you mean 1 zone with 4 emitters. Or maybe it's just indicative of the loads that they all come on together even though they are seperate zones.

brewdesign

Gordy, thanks. That is my bad for the terminology used. One zone with 5 total emitters would be the correct statement.

Since it is on an outdoor reset, the actual BTU requirement for that zone ranges from around 2K BTU to 14K BTU.

Using the hydronicpros buffer tank simulator with boiler running at 160F supply / 140F return at minimum 2K BTU load, I come up with boiler fire times of 2 min on and 47 minutes off if the "buffer" volume is 10 gal (I'm counting boiler [3 gal] and indirect water heating water [6-8 gal] as the buffer here).

At 14K BTU load, times look like 3 min on and 7 min off. That in itself seems to be borderline excessive but the real buffer volume in the drawing would be significantly more than 10 gallons if the 40-60 gallons of DHW heat is flowing "backwards" into the heating water chamber. Ideally, this backwards heat flow would satisfy the 14K BTU load until the DHW temp was low enough that the tank aquastat calls for heat, making the radiant heat zone more or less invisible to the system.

In the drawing, I can't see that the sustained minimum boiler temp will be under 110F to maintain condensing mode in a mod-con unless maybe both fan coils are running at the same time. That scenario would create a heat demand in excess of boiler output if the boiler is matched to the building heat loss, approximately 50K BTU.

brewdesign

hot rod said:

what about a hydro-sep at the boiler. Gets you air, dirt, magnetic, and hydraulic separation for the entire system.

Thanks for the drawing. It seems like the hydraulic separators have become really popular, I don't recall seeing them a few years ago.