DHW Priority...

Tom S.

I'm having a dhw indirect tank installed to replace a standalone dhw tank which is at the end of its life anyway. I've got 2 zones off of my boiler now and the indirect would be the third.

My installer is not a fan of priority for the DHW and therefore does not see the need for the zone controller with priority for the dhw zone (taco controller). I've read here that people like the idea of priority, and I know the taco has a switch so you can toggle it on/off anyway. However, the addition of the zone controller and time to wire it might add $500 or so to the price.

Is it worth it?

Thanks

John R.

Unknown

I usually

prioritize, the result is a smaller boiler so less fuel consumption. Don`t know what you have now, but if not, make sure it can handle everything at design temp.

Dave

Tom S.

How would

I figure out if I can handle everything at design temp? I have a W-M 131kBTU boiler and a 2200sq ft house. Do I need to do heat load calcs etc?

Thanks

John

ALH_4

Heat Loss

I agree with Dave.

I think it would be a good idea to do a heat loss calc. Slant Fin offers a free program for this purpose. There is a link at the top of this page.

My guess (and this is a complete guess) is that if you have average insulation in your home, you have nearly twice as much boiler output as you need. If you have poor insulation and single pane windows, you may have the correct size boiler for your heat loss. It's a complete guess without a heat loss calculation specifically for your home.

Tom S.

Thanks for the answer. In your complete guess scenario, if I have a boiler that is probably oversized, do I need priority? I realize this is somewhat of a WAG, just trying to understand better.

And lastly, assuming priority isn't essential, is a zone controller "box" of any value? Right now I don't have one, just a fair amount of wiring which I figured the zc box would neaten up and make more serviceable.

Thanks

John

ALH_4

Relay

If your boiler is significantly oversized, or you do not mind if DHW recovery is slow, priority may not be necessary. I assume you have zone pumps. At the very least, it is a good idea to install a 3-zone pump relay box that has a priority switch for the DHW zone. It does not add much cost over a relay box without a priority zone.

Beyond that is an upgrade to a Tekmar 260 for maximum fuel savings and DHW heating with your equipment. It has outdoor reset for the space heating zones as well as DHW priority.

Tom S.

zones have zone valves, one circulator for the whole thing. The indirect would get its own circ. I think that answers the pump question above....

Anyway, sounds like it is worth putting in something like the taco zone controller box (I assume this is a relay box like you talk about) with the on/off priority switch for the dhw zone.

Thanks to both of you for your replies.

John

ALH_4

One last thing

IMO, your plan is the best way to pipe it. A Taco PC700 plugged into the switching relay will give you the best of all worlds. A differential pressure bypass valve may be necessary on your heating loop depending on the pump that will be used.

hr

Unless you pipe and pump

the indirect corretly, you may not even utilize all the boiler output. So if you prioritize make sure the pipe size, zone valve or circ can move the btus the boiler can put out.

It is really more of an issue how much DHW and how fast. If you have a large tank, one dump load then time to recover, and enough boiler to drive the heat zones at the same time, then skip the priority.

One issue is extended priority cycles. Some controls have a time limit so a DHW call doesn't keep the heat zones off for extended periods.

Really need to look at the big picture, heat load, actual boiler output, desired DHW output, etc.

hot rod

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Doc Radiant

> the indirect corretly, you may not even utilize

> all the boiler output. So if you prioritize make

> sure the pipe size, zone valve or circ can move

> the btus the boiler can put out.

>

> It is really

> more of an issue how much DHW and how fast. If

> you have a large tank, one dump load then time to

> recover, and enough boiler to drive the heat

> zones at the same time, then skip the

> priority.

>

> One issue is extended priority

> cycles. Some controls have a time limit so a DHW

> call doesn't keep the heat zones off for extended

> periods.

>

> Really need to look at the big

> picture, heat load, actual boiler output, desired

> DHW output, etc.

>

> hot rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_

Doc Radiant

"One issue is extended priority cycles. Some controls have a time limit so a DHW call doesn't keep the heat zones off for extended periods."

IMO, the use of this feature is a must if you are going to prioritize DHW. If the DHW circ goes bad and the zone is never satisfied, the heating zones will not come back on. We had that happen once years ago with one of our customers - luckily the weekend they went away was not below freezing.

I would prioritize (with priority over ride), pipe/pump it for full capacity and let 'er rip.

Darin Cook_5

WOW

That boiler you have could handle a 60 btu per square foot heat loss. That kind of heat loss is usually in a lean-to up in the mountains. But that being said, you have alot of firepower to generate hot water. How much hot water are you looking to make?





Darin

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Tom S.

just a family of 2 adults and a little toddler. No hot tubs or other big things - bath for the toddler, shower for the adults, general domestic use otherwise (dishwasher, washing machine, etc).

I inherited this boiler from the previous owner...If 60 btu/sq ft is a big number, what is a typical house have for heat loss? I will probably try to do one this weekend with the slantfin software, just curious what is a typical range. We have new windows in the house so that's a bonus too.

Tom S.

I see the issue with extended priority. I was looking at the taco 4-zone controller with priority (zvc404) but I don't think it has a timeout for the priority mode. Does anyone know if it does or doesn't? And if not, is there a product you know that does?

Thanks

John

Bruce Marshall

John,

All Taco multi relays are equipped with priority but if you want to add outdoor reset with the PC700 or a priority protection card (PC600)you will need a ZVC404 EXP relay. The EXP gives you many more features.

Bruce

Tom S._2

Ran a quick heat loss calc - probably made some wrong assumptions, hopefully they were on the conservative side. I did use a zero degree "outside temp" for New England winters.

I realized the sq feet is more like 2500 b/c of some unfinished but heated space in the basement.

Came up with a heatloss of 91k, which is approx 36 btu/sq ft. I guess that sounds more in line with 1960s construction.

Assuming that is approximately right, and I have a 131k boiler, I would think I have room in the boiler to not worry about priority.

John

Joe Brix

I'd listen to Bruce

and look for outdoor reset also. With zone valves, I wouldn't worry about timing priority. Usually if the zone valves open by the thermostats. You will still get some ghost flow. The rads don't go stone cold on you. Find a good hydronics guy and see if the boiler can be down fired a bit, Sizing the boiler to the load saves you the most oil. Spring for the Tekmar 260
get outdoor reset and priority control system.

dana_3

priority

with hot h2o priority. at 6am when dad gets up to take shower , then mom gets up to start getting the little ones up for school and showers. it's now 7am. now dad is feeding the kids. mom now throws aload of laundry in. now she jumps in to take a shower. it's now 7:30. after cleaning up the kitchen, the kids, and the dishwasher it's now 8am.your house is now GETTING COLDER, because of hot h2o priority. this is why you don't want and shouldn't use priority. your taco zone panel doesn't give you timed priority. with a properly sized system. hot h2o priority should never be an issue