Thoughts on VT2218 circ for on modcon setup

canonman

Boiler is a Velocity Raptor 155, 10:1… Run times are good, but always looking to extend and get even more efficiency.

Had a Taco circ pump go out on me which started a bunch of reading on newer circ pumps. I am going to swap the boiler circ for a 007e (manufacturer recommended) and keep the old one as a spare.

Some time ago, someone moved boiler from inside the house to out in the garage. There is roughly 20ft of 1 1/4" pipe to the baseboard zones, 5 in total. The in-floor zone (2 zones) manifold is in the garage.

My question is… would swapping the taco 0015 with a VT2218 (running deltaT) be advisable with a modcon and outdoor reset? Let me know if more information is needed.

SuperTech

I have a couple of VT2218s on my boiler, they are great circulator and I love the different modes of operation that they offer. It's great for dialing in the flow rates that you want. I don't think you have a whole lot to gain by using the delta T mode with the outdoor reset. Let the outdoor reset control the boiler temperature. With all those zone valves a variable delta P circulator like the Taco VR1816 or Grundfos Alpha would be more appropriate.

Kaos

With a modcon you want as much delta T as your unit allows. The efficiency of a modcon is pretty much determined by the return water temperature to the unit, you want this as cold as possible. See my post here:

https://forum.heatinghelp.com/discussion/198291/is-it-bad-if-a-modulating-boiler-never-runs-deep-into-the-turn-down-ratio-or-high-in-its-capacity

Outdoor reset helps but you can do even more by setting your flow rates correct. This is a win/win. Less fuel use and less pump electricity consumption.

Delta T is one way, Delta P circ with properly adjusted zone setters also works. One thing to watch, at least with the older Taco delta T pump I have is that in delta T mode if any of the sensors come loose it simply shuts down (of course this happened in the middle of night in winter). Don't know if they fixed this in the newer one.

canonman

Appreciate the input. The more I read, the more opinions I get, the more conflicted I get :) Part of me wants to dive into setting up a DT, but I'm not sure if I have the time it deserves.

I appreciate the help so far.

Dave H_2

The VT2218 on a baseboard system with zones and outdoor reset works great. The circ does not care what the supply temperature is, only the delta T it sees. It does not need tending to not much programming, it comes out of the box set for a 20 degree Delta.

When zones open, the circ will speed up, when they close is slows down. When it gets cold outside, it speeds up and when it warms up, it slows down. It will help that boiler see colder return temps allowing it to condense more. A delta P pump will speed up and down when zone valves open and close but it will not change speeds based upon the temperature outside changing. same flow in each zone all year round therefore the delta t starts to shrink as it gets warmer outside.

As Kaos queried, yes an earlier version (12 years ago), if the sensor got disconnected, the circ would shut off. If this happens to the VT2218, the circ would run full speed and the screen will flash for someone to notice but you will have heat no matter what.

canonman

I have a 2218 on the way.

Dave… one question. On one of Taco's webinars, I remember some mention of the boiler circ running less flow than the system circ. If DT slows down the system circ, is it an issue if the boiler circ is running at a constant flow greater than the system?

hot_rod

From a thermodynamic standpoint, here is what goes on with a constrained ∆T operation.

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Dave H_2

https://forum.heatinghelp.com/discussion/comment/1818769#Comment_1818769

@canonman Yes, we have discussed this situation and it does happen often in systems especially when the lowest modulation of the boiler is still much larger than the zone that is calling. When that happens, the return temp to the boiler increases and short cycling of the boiler increases. Variable speed circs on the heating side can help that and boiler circs that are varying their speed based upon the needs of the boiler can also help with the short cycling.

There are some boiler manuf that want to control the speed of the circ to benefit the temp0 drop across the heat exchanger. Others are starting to go into detail on what circ to use (and what setting) in order to achieve the desired temp drop.

hot_rod

On my Lochinvar, the control operates the boilers pump speed. It is not a fixed delta operation, I can hear the pump constantly changing speed.

But to be honest in it's quest to keep the efficiency up, lowest RWT, wide ∆, it does slow down the heat transfer. I'm all for efficiency, except when my building is cold and uncomfortable as a result. Slows down the pump when I need max. output. Constrained ∆ operation does this also.

There is a place for fixed or constrained delta operation, but I don't think that it is the best distribution pump option.

My shop overhead door is open today, sunny 60F outside. When I close the door and turn the boiler back on I want fast recovery, full boiler output, constantly running until it catches the load. My boiler will boost output temperature if it is not catching up fast enough. I don't want my pump slowing down.

For efficiency I'd spend $$ on a reset control, as temperature modulation is very linear. Flow adjustment to regulate heat output, not so much.

tekmar example.

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