Using TVR's

Rich Davis_2

Im thinking about using TVR's to control the hwbb in my house.  I would use a TVR for each space.  My question is how do you control the boiler (mod-con with ODR) and the circulator.  Would I still need a regular thermostat?  Thanks

Devan

A thermostat

in the largest room (heat loss) could be one way.



You can also use a setpoint control from Tekmar, that will turn on circulator off of outdoor sensor , and shut off at warm weather set point of 65* F or so. Boilers' control will operate independent , based on fluid temps.



TRV's set at desired comfort. However using HWBB would mean a re-pipe home run to each room to adapt TRV if current HWBB is looped.

Gene Davis_3

Clarify, please

"setpoint from Tekmar . . . outdoor sensor . . ."

Please help out this dummy who is trying to learn something about these systems of mod-con-produced water, and TRVs on each emitter.  Heating is not my business, designing houses is, but I still like to know something about these mechanicals.

Are we talking about outdoor reset?

Alan (California Radiant) Forbes

Outdoor Reset

I believe Devan is talking about a system that instead of an indoor thermostat, an outdoor sensor will turn on the heating system when the temperature drops below 68 degrees.  This same system will modulate the water temperature as a function of outdoor temperature; the colder it is outside, the hotter the water being delivered to the emitters.  Ideally, if the radiators have been sized properly and the controller programmed correctly (reset ratio and parallel shift), the output of the radiators will match the heatloss of the individual rooms.  In case the radiators are too large, the TRV's will prevent overheating.

Devan

Alan is right.

Is it Gene or Rich?

Tekmar controls allow you to have room(air)sensors or auxillary sensors or both that can come on and off .

MikeT_Swampeast_MO

TRVs

Thermostatic Radiator Valves do one thing--and they do it very well--they LIMIT heat by regulating flow based on a single sensing function (usually room air temperature).  They contain a regulating valve that can restrict flow but once fully open they can do nothing to "get more heat".  In other words, they must be supplied with at least enough energy to maintain the desired setting--they can reduce the available heat but they cannot do anything to get more heat.



TRVs work best in two-pipe systems that find a dedicated supply and return pipe to each and every TRV equipped emitter.  What this really means is that each emitter has the same supply temperature available for limiting.



Baseboard systems are most commonly a form of one-pipe systems that usually finds baseboards in different rooms connected end-to-end with the first served having the hottest water available and each subsequent baseboard having a lower available supply temperature as each baseboard removes more and more energy from the supply.  It is essentially impossible to install TRVs in such a system that serves multiple rooms.  If you use more than one TRV in the loop things will go utterly crazy.  Even if you use only one TRV for the entire loop, there will almost certainly be extreme temperature imbalance between the rooms--regardless of which room contains the TRV.  For this reason nearly all baseboard systems require significant piping changes to use TRVs.  The most certain way to do this is to re-pipe into a true two-pipe system.  Bypass lines can be installed around baseboards, but care must be taken in sizing and running the bypass lines to ensure that each baseboard still has sufficient available flow and that some baseboards don't wind up "starved for flow".  Even with ideally sized bypasses, such a system usually won't have the full adjustment range and high control accuracy associated with two-pipe TRVd systems.



The ideal way to control a fully TRVd system is with a system that finds constant circulation whenever heat is required with a supply temperature that increases with increasing system load (like falling outside temps).  In other words, a constantly circulating system using reset (usually outdoor reset but sometimes indoor reset) and warm-weather shutdown.



The actual control system will however vary depending on the system and especially the form of boiler and (especially with condensing/modulating boilers) the internal control theory of the boiler.  Since TRVs aren't particularly common in the U.S.A., their internal control theory is often geared to multi-zone systems using separate circulators or on-off type zone valves that often require different supply temperatures in different zones.



As a home designer, if you would like to suggest a system using TRVs, I would highly suggest that you specify two-pipe systems with ALL emitters not only identical in general form, but sized to operate at the same general supply temperature.  This allows for the simplest general system that will maximize the efficiency of condensing/modulating boilers.  While certainly more expensive than a typical 2-3 zone one-pipe baseboard system, it can be less expensive (and efficient) than elaborately zoned systems using many wall thermostats and often extremely expensive electronic control systems with propietary components.