Please Critique My Schematic

I wonder if anyone who's interested could please review my schematic, created in Taco's HSS (.hvp project file available upon request). I based it on the Tarm schematics for a Pellet Boiler with storage, hydraulic system 2.1, and for the pellet boiler with Energy Tank, hydraulic system 1.1, below.
( http://woodboilers.com/images/stories/documents/p4_pellet_plumbing_schematics_8.5x11.pdf )

Several things:
-DHW not detailed
-Water addition, low level protection, etc, not yet represented
-I couldn't really figure out how to model the reverse indirect, which has 118 gal on the tank side and 11 gal in the dhw coil. It does indeed create big btu/hr draw-33k plus at 1gpm dhw flow
-The boiler outputs, pump gpms, head losses are CALCULATED based on the imposed baseboard loads, which come from measured baseboad lengths and characteristics and estimates of piping lengths.
-Attempted to model existing system, with location of expansion tank and air separator.
-Boiler pumps are new

Observations:
-The flo-chks add 1.5 ft head loss each
-It says the air separators adds 3 ft head each

Questions:
-The main question is: Will this work?
-Can I get maybe get away with one air separator, like a Spiro, by the pellet boiler and delete AS-1? They'll only be 6' apart or so, and the pellet boiler will be on most of the time.
-I've read that expansion tanks should go upstream of the pump. I did that with new ET-2 which should be larger than shown because ET-1 is really 4.4 gal, not 6.2 gal. Since I might be deleting AS-1 (original air scoop), I could also delete the original expansion tank, ET-1, and enlarge ET-2, so that they'll be upstream of the boiler pumps.
-Would auto pressure feed pumps be the way to go since there are three changing loads? Thing is, you would want excess boiler capacity to charge up the EnergyTank, but even only 1gpm provides 45,000 btu/hr. I'm leaning towars an auto pressure pump, e.g., and EcoCirc Auto.

Thanks.
VF

Clarkbug said:

One air separator will be just fine. Keep the AS-2.

Expansion tanks should be located at the point of no pressure change in the system, if possible.

Your energy tank shows a leaving water temp of 150, other loads are at 160. Dont know if that changes anything within the Taco software.

Do you need return water protection for the new boiler?

The autocirc works best with zone valves. In your case, each zone having its own circ really makes that less than the best case scenario. Variable speed so you can dial them in is good, but the auto feature might not pay back anytime soon.

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-So, would the AS-2 location before the pellet boiler pump be okay?
-I did set the -30 delta-not sure why-I just removed it.
-Not sure about boiler protection. Tank will probably be set at 145, and it's 119 gallons total, so I'm thinking not.
-I was talking about the boiler pumps. One heat zone or the other could be on, both heat zones could be on, no heat zones might be on, and the buffer tank might be calling for heat at anytime; I figured all those variations would do well with a auto circ feed.

Thanks for your comments Dan.

Hydraulics is not my thing, but what I see is:

The energy tank would always have flow whenever there is a call for heat and the boiler circ is on, so the tank temp would routinely be at the boiler supply temp when there is call for heat from the baseboards. Maybe OK for the pellet boiler but not so much for the oil boiler.

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-The baseboards would draw heat from the energy tank until the tank gets to a certain temperature at which time the pellet boiler circ pump and the pellet boiler fires up. The oil boiler would be kept out of the mix until the pellet boiler is ascertained not to be producing heat. Although the pellet boiler might be a tad undersized for design day, I don't foresee having the oil boiler come on to augment the pellet boiler's output.

There could be a hydraulic imbalance between the zone circs and the boiler circs, giving unintended ghost flow. The control scenario for the zone circs is not indicated (fixed speed, fixed delta T ?).

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-There are check valves which hopefully address the ghost flows. The zone circs are EcoCirc Varios, which have stepless manual speed control; they are straight replacements for the existing Taco 007s. The circs go through an Argo zone controller, turned on and off by a thermostat in each zone. The boiler feed pumps will be the source for the Energy Tank "zone". As I originally said, I'm leaning towards an auto pressure pump for the boiler feeds because of the changing loads.

The reference designs clearly show the three way mixing valves for the baseboard loops which could easily be motorized operators and OAT reset. This is the biggest thing missing imo. If you implement OAT reset of the loop with VS injection pumping and primary secondary, you may be able to implement the boiler return protection feature of the reset controller. It will not load the loops until return water is up to temp and ramps up load as HWS is available.

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-That's something to think about, but the buffer tank makes up for the on/off nature of the circ pumps. What do I care if they cycle-the boiler's not coming on until the buffer tank's temp gets low. I'd like to continue to use the wood insert a fair amount, so the total heat load might easily get below the 30% modulating capability of the pellet boiler. I'm not so sure if return protection is required, since the energy tank will be 145 and the zones are only low-volume baseboard, not a slab or big radiant floors. There will be no extended low temp times.

Reset will allow the pellet boiler to operate much longer in its modulating range, as state earlier.

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-I'm not so sure this is much of a factor with the buffer tank.

Boiler return water protection scenario is not shown or implemented. The Wjndhager would have to be rated for low return water temp and it is not at all clear that the Energy Tank as shown can keep the Windhager above its condensing temp.

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-We're not talking big slugs of water, and I'm not letting the tank get too cold. Maybe a scenario where both heat zones were on, the boiler was off, and there was an extended DHW call (there is 119 gallons of buffer). The ramp up time for the pellet boiler would consume some of the Energy Tank heat, and maybe you'd run out of water, unless priority was engaged (a mode in the zone controller shutting off the heat zones in favor of a dhw zone) in some way-maybe engage at a temperature lower than the boiler set point, indicating that it wasn't keeping up. I don't see this scenario happening too much though.[/quote]

Why you would want to keep the oil system is a mystery for me. It costs money to implement and maintain the oil backup system. My thinking would be to put the oil money into a savings account and maintain a cash backup, so if in the future the Windhager is down for service the alternate is not the oil burner but spending cash from the savings account to get the Windhager back up running. This is the whole idea behind buying high quality equipment that is long term reliable and serviceable. The oil burner is not shown on the TarmUSA reference designs.

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-See drawing 2.1, above, which shows the oil boiler. I'd do it for peace of mind. Hey, I already spent the money for a new flue.

Do you plan year round DHW from the Energy Tank?

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-No I plan on installing a GeoSpring hybrid water heater; the dehumidification aspect is appealing.[/quote]

My changes would be: no oil backup system, 100% pellets with maybe an alternate non hydronic temp heat source, wood stove or minisplit, absolutely OAT reset VS injection pumping with boiler return protection scenario (similar to the Tekmar 360-361), fixed delta T for the VS loop pumps.

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-I will look into that more.

You probably want check valves or heat trap piping in and out of the Energy tank to trap heat but I don't know how this affects the system hydraulics of the tank being on all the time.

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-That's a good point. I can see for the DHW piping for sure. I don't think they'd be appropriate for the Energy Tank source because its flows are two-way.

http://tekmarcontrols.com/products/hvac-systems/360.html

http://tekmarcontrols.com/products/hvac-systems/361.html

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Thanks again for the comments.

Thanks for looking, again.

Yup, keep AS-2. That way no matter what boiler is on, you are going through an air separator.

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Thanks. That's the way I figure it.

Figure out your boiler protection scheme. If you use a lot of DHW or you have a zone that was sitting, thats a slug of cold water that will hit your return. You can use controls or a tempering valve, but I would see what Biowin says. Thats important for the warranty.

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Marc answered this I believe, but if there were to indeed be prolonged use of DHW where the tank got pretty cold maybe priority could be switched on to turn off the heat zones. Not sure if this scenario would come into play though.

Buffer tank always gets flow, right? So no change in pressure/friction there for when the boiler pump is running?

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True. But both of the heat zone pumps are on and off and the boiler pump will at some point simulataneouly be on. I'd think a pump like the EcoCirc Auto could react to that.

Thank you very much for checking it out EW.

ewdudley said:

As has been pointed out previously, your pellet boiler wants to see a load that is relatively constant and that changes gradually. The boiler can modulate down to 30% (IIRC) and will perform best if starting and stopping is minimized..

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As I noted earlier, for significant amounts of time I will be below 30% of total boiler output because of a wood insert, and hence the buffer tank. But I do think I like what you and Dan seem (to me) to say: that it would be good a good thing if the water temperature going into the zones was adjusted to the system requirements as indicated by the outdoor temperature. That it would increase the average amount of time the unit is able to operate continuously, even with the use of a 119 gallon buffer tank. What would you suggest as the easiest way to do this, a outdoor reset mixing valve like Taco makes?