Dual Setpoints??

heatboy

there is a supply sensor on the mixed loop which will tell the control what to do with the mixing device (be it a valve or pump), so no matter what the boiler temp is the radiant will always maintain it's own "curve". Boiler supply temperature should be 10° to 20° above your mixed temperature needs to assure adequate temperature control.

hb

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Dave_13

2 temp setpoints?

I am just a wanna be radiant junkie, but I have a question on temp. setpoints. If you have a system that requires 2 different water temps, is it possible to feed the boiler 2 different setpoints? i.e.- If your floor is calling for heat, then run at low temp. If BB or DHW, then run at high temp? Does a mixing valve modulate on temperature? My thoughts were if it does, then you could put one on the radiant in case both low and high temp zones are calling for heat. Is this ever done or am I just a freak!!!!

kf_2

Your right on...

some boiler and control manufacturers allow you to set one heating curve for the boiler reset, and an entirely different heating curve(s) for 1 or more motorized mixing valves. All by the way, usually running off of 1 outdoor temperature sensor.

This method also protects the radiant zones for boiler temp spikes when there is a call for DHW production.

kf

Dave_13

Do normal mixing valves adjust ratio by temperature or are they based on a fixed supply temp and the ratio is always the same????

kf_2

they are...

adjusted by temperature. The needed supply temp is usually adjusted every time there is a change in outdoor temp. The heating curve is the ratio. For instance a 1.2 heating curve would supply approx. 150 degree water on a zero degree day. Every time the outdoor temperature goes up 1 degree the supply temp lowers 1.2 degrees.

Some controls pick the heating curve for you after you enter the design supply temp and the design outdoor temp.


kf

Dave_13

So...

lets say you had a 2 setpoint point system. If your radiant zone was calling for heat at say 110 F (boiler supply running at 110F), and then BB zone called for heat at 160, and your supply went up to 160- would the mixing valve on the radiant hold that zone at 110??? Would it automatically compensate?

Ted_5

DHW priority

will shut off the heating pumps and ramp up boiler temp and
after the call is over the mixing valve will protect the
radiant floors. You could also get multiple temps by having
one motorize proportional 3 or 4 way mix valve and down stream of that valve have another proportional nonmotorized
3 way mix valve.

Ted

Boilerpro_3

Can be done using one reset curve

You can use a single reset control that is set for your highest supply temp needs...say 140F for radiant under wood floors. Then you take this mixed down water and mix it down again with a fixed proportion mixing valve or injection loop for you lower temp need....say a garage floor that needs 85F water. As the higher temp water resets from 80F on a warm day to 140 on a cold day, the lower supply temp water will also reset from about 72F to 85F. I believe Ted is referring to this type of setup.

Boilepro

Henry_9

For fear of sounding like a commercial

This is one of the reasons for seriously considering Viessmann equipment, the concept of total system integration. Not only are we resetting the boiler and a secondary temperature, but integration is seemless and by one manufacturer.

Furthermore, as so well stated by Ted, I can add in more integrated reset stations for more temperatures. I can add in DHW production, external demand for pool - spa - snowmelt and it integrates right into the tempertaure logic of the system, without a temperture hiccup the user to contend with.

The system becomes more than just the sum of it's parts. The benefit to the contractor is simplicity of installation of course, but simplified serviceability and far more importantly, repeatability.

How many times do we reinvent the wheel to accomplish similar tasks job after job? Seemless integration means doing it everytime, utilizing the same fundamental concepts and basic tools over and over. It is just like shooting free throws, always the same. Good fundamentals breed success.

I love this industry!

Henry

V-Team

Unknown

look what was just published this month

just what you asked for, by the master.

http://www.pmengineer.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2732,101268,00.html