tweaking a reset curve

Bill Nye_2

Not as up on the 260 as I should be.... but. Does it have a parallel shift dial? I have a Viessmann and I am dialed in really really close on my reset curve , BUT, if we have sustained weather below 20° or colder for several days I need to turn up my parallel shift a few degrees to keep the room @ 68°.

Just like adjusting a t-stat really. It takes one second to do. My house is of irregular construction from different time periods.

I wouldn't be too concerned. Take a good educated guess, [you already have] and adjust from there. You have to live with it for a while to tweak it in.

Rob_32

tweaking a reset curve

Heat loss shows 50k BTU/hr loss at design day 5F OT, 70F IDT.

Room by room loss calcs suggests that emitters can produce sufficient heat to meet the loss at 165F supply temp (i.e., there is slight overradiation so don't need 180F water).

So the question is, for a tekmar 260's curve, should I set the BOIL DESIGN to 165F since it is at that point which the loss meets the input?

On the light loads to date we are not quite at constant circulation, and I think this downward shift would get us there.

I believe this is a viable approach, but opinions would be welcome.
Thanks.

subcooler

Save your equipment

Allow you equipment to overshoot a little and cut down on half of your yearly run time and cut your cycle rates in half.

Perry_2

Not familiar with your equipment' but...

My Viessmann Vitodens 200, with outdoor reset - and indoor "RS" controller - automatically tweeks the reset curve up or down as approproiate for maximum boiler and system efficiency - and maintain desired house temperature.

I have cast iron baseboard with a monoflow T system.

Perry

Rob_32

relationship?

Not sure I understand that relationship. Small percent overshoot cuts runtime in half?

subcooler

You need 50k

and what size is your boiler? 100k, 150k 200k. Most boilers never run more than about 30% to 40% in heating applications. So cut your run time in half by overshooting, yes been there, do that all the time.

Wayco Wayne_2

What kind of

boiler do you have? What is it's capacity? The Tek mar 260 has built in time delays so a cast iron boiler doesnt cycle too often. I say go as low as you can. Go 160 and see what happens. (how low can you go???) If it's a cast iron boiler keep the bottom at or above 140 of course. WW

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Perry_2

Wayne

It's a Vitodens 200, 6-24.

This is a Stainless Steel modulating condensing boiler - made in Germany. Minumum heat output rate of 22,000 BTU per hour - Maximum of 73,000 BTU per hour (they have larger models as well). Not cheap either; but when I looked at how best to minimize my fuel bills with what could match my heat load requirments - and how it would connect to my 1950's monoflo T system. Toss in heat load variations from thermal gain and windy day heat loss - the Vitodens had all the answers as readily available optional components. Low Loss Header, RS controler, and lots of built in features with the Vitodens 200. It was really the best option I found.

I also believe that it will be a very durable long term unit; and am skeptical of some of the other smaller mod/cons out their (I may be wrong at that - but how long are o-rings and AL really going to last?)

My secondary circulation temperature has varied between 85 F to about 110 in the last several weeks that it has been installed (I will probably need it to reach about 140 F - perhaps a bit more on the coldest days). It has held the house to within about 1/2 F where the RS controler (thermostat)is mounted. Rock steady house temps.

I have yet to enable the nightime house temperature setback feature. That is something for me to do after my power plant outage.

The noisiest part of the system is the Taco 007 secondary circulator.

I can 't wait to see the small gas bills show up

Concerning the cost: The Value of low gas bills will be frequently remembered long after the installation bill is paid.


Perry

Rob_30

specs

Boiler is a Burnham Revolution RV4. 73k IBR.

How much of an overshoot, and how to achieve? Just bump up the design temp so we get hotter water than necessary?

Rob_30

Wayne

See above specs.

S Ebels

Tweak is the operative word

You do just that. Tweak. Make your adjustments in small increments, like a degree or two at a time until your reach a point of constant circ and you're not keeping up. Then give the control a nudge upward to meet your temp and leave a little overage for coming out of setback.
It's really a matter of your own personal preference and it's not like you're going to screw anything up by going to low. If your boiler is of a type that doesn't like low water temps, you'll need to establish that temp as your base level and go from there. (What boiler are you working with and what's the input BTW?)

Letting the boiler overshoot by a large margin decreases comfort, efficiency and if you have typical baseboard, the stuff will be creaking and groaning all day as it flip flops between 120 and 180 water temp.

Rob_32

sounds good

Thanks. Burnham Revolution. 96k input, 73k IBR. Typical baseboard. Can't believe how well it does with ~115F water.

Will do.