Ultra and Snowmelt

Darrell

Here is a situation that I keep running into and am asked for input on, although I do not do new installs, I do help design control stategies for some of the contractors...and then I get to service them.

Ultra boiler, radiant floors, WMC domestic indirect, and snow-melt. The contractors are being told to pipe the snowmelt on the DHW side of the Ultra and let the Ultra do its thing for the radiant on the space heating side...which it does well. The problem is that the DHW has priority, so when the snow melt calls for heat...the space heating side of the Ultra is off until further notice. The control strategy is to install an on/off relay timer that, when energized, runs the snowmelt for a set time and then cycles off for a set time, and then back on and then back off until the snowmelt switch is turned off by the owner. The theory being that during the off cycle the space heating can catch up from the "DHW" priority soft lockout. It makes for a wiring nightmare. One very real possibility is freezing the heatexchanger or tempering tank if the snowmelt circ is not shut down as well. I'm not sure that any effective heat can be transferred to the snowmelt in an on/off cycle while maintaining the space heating without dropping it too far.

Any good ideas? So far WMC has promoted the timer/relay as the fix, and claim to be addressing the issue in an upcoming model of the Ultra. Bear in mind that we routinely run snowmelt at temps as low as zero or minus ten!

GW

I don't know much about the Ultra, you can't disable the priority? Yukky. That seems lame.

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hr

How much snowmelt can you

actually drive without a grossly oversized a heating/ dhw boiler? Seems a dedicated boiler for the snowmelt would be better.

Although all the mod cons have exercise and freeze protection built in which makes snowmelt controls a challange even on dedicated snowmelt boilers.

Be sure you use a good AL glycol on those ultras. The inexpensive brands merely have a ph buffer and not all the extra ingrediants to truely protect the aluminum.

Nobel No-burst al is a good one, or the Rhomar brand.

hot rod

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Unknown

I'm with HR, unless this is a very, very small snowmelt area.

In general I would want to use a snowmelt controller and mix for the snowmelt, so you can soft start the system, protect the boiler against freezing, etc.

Also I think the Ultra among other mod/cons is only rated for 35% glycol mixtures... be careful. Normally I like to see 50% in snowmelts, which means it's heat exchanger time..

of course I just added about $1000 to $2000 to your system cost. aren't I helpful?

Dave_4

P 42?

Does setting parameter P 42 to '0' shut off priority? It isn't a recommended setting according to W-M and the wording is odd in their lit, but this may be it.

Darrell

I don't think so...

As I understand it, the DHW priority lockout is necessary because the Ultra uses the same block for two things...DHW and Spaceheating, which is regulated on an entirely different set of parameters. If the Boiler was allowed to switch back and forth or do both at the same time the spaceheating could get too hot or respond strangely. So, WMC makes the DHW priority lockout the spaceheating so that overheating cannot happen. When the Ultra switches out of soft lockout, back into spaceheating, a purging takes place to ensure that the block is clear of over hot system fluid. It makes sense, but these contractors are being encouraged to make the Ultra do something it was not designed to do...with at least a wink and a nod from WMC. The timer lash up limits the time that the "DHW soft lockout" can go on. As far as I know, as I am being told by the local WMC Rep, there is no way to override the DHW priority, 'cuz that would screw up the space heating curves and safety features.

If they were to hook up the snowmelt to the space heating side, say into a 20 gallon tank, the length of run time would cause the Ultra Brain to ramp up the space heating supply side temps...and there goes the curve and safety features.

Quite honestly, the only snowmelts that I see that I can depend on to work and do their job are simple cast iron boilers with off-board snowmelt and staging controls by tekmar. If a person is heating the great outdoors and melting snow...efficiency isn't the driving motivation! I do see a couple of systems that are mod/con driven into primary/secondary piping and then the controls are also done off-board. This allows the boiler, or actually, both boilers to stage and modualte to satisfy the load whether it is space heating only, DHW, or snowmelt, or any combination of the three.

But, what do I do with these existing systems?

Drew_2

Antifreeze %

First,
Hot Rod, Thanks for the kind words.

Second,
There may be some confusion about antifreeze %s.
When a manufacturer of a boiler states 35% for the antifreeze, they are reffering to the propylene glycol content. An example is our Noburst -100 product, when mixed 50/50 you will have 35% propylene glycol in the fluid. If you used our Super Noburst at the same ratio, you will a 49% propylene glycol fluid.

Drew/Noble Company

Guy_6

switch

Can you make the current DHW side the HEAT side, and vice versa, thus prioritizing the HEAT? If you are using the outdoor reset, the radiant side is getting a little benefit, but in this case I would think that it is worth losing. With that, the outdoor feature would actually help in controlling the snow melt by disabling it in warmer weather. Split the new heat zone with a 2 zone priority relay, and the DHW takes full priority, followed by the heat, and finally the snowmelt.

Guy_6

Hmm

Having just read Darrell's post, I may have spoken out of turn;my knowledge of the W/M control is limited. As far as I know, the control in the boiler simply has two sets of operation built in- one single temp priority, and one reset temp. The purge feature is great, but if it is in the way, it can be worked around.