Radiant system with no thermostat

ALH_4

Once you get your heating curve "dialed in" the boiler can track the heat load very closely most of the time. However, the same heating curve may not track as well during spring and fall as it does in winter. Personally, I feel the ideal setup is to couple indoor feedback from each zone with outdoor feedback at the boiler.

There is the RS indoor temperature sensor for the Vitodens, but this only measures the temperature in one zone. If the home is small and the floor plan is open, this may be fine. How well the system you describe can work is very dependent on the diversity in the heat load from room to room.

At the very least, provide some method of manual flow balancing to your zones. It is impossible to predict the actual heat load and solar gain of a room from year to year.

Personally, I would still install non-electric thermostatic valves (TRV's or FHV's) that open in proportion to the temperature in the room.

dblagent007

What about wind chill

I am in the process of designing a radiant system that continually circulates and uses the Vitodens 200 as the boiler. I am going to install it without any thermostats and rely on the heat curve in the Vitodens.

I know the Vitodens has an outdoor thermometer, but how does it maintain the appropriate temp in the house and still account for things like wind chill, insulative value of a foot of snow on the roof, etc., etc. Will it really keep my house right at the temperature I want?

Brad White

Wind Chill

really only applies to mammals that perspire. Your heat loss, if per ASHRAE method and I think Manual J, accounts for a 15 MPH wind and the infiltration at that point. That in turn should be reflected in your radiation sizing.

(Absent a blower door test, infiltration is just a guess and an average anyway. That is a whole' nother subject.)

I can tell you from personal experience that the Vitodens tracks heat loss exceptionally well without an indoor sensor. I intend to add one this year to see the difference. We have TRV's on all radiators but three (bathrooms and one we cannot get to neatly). To tell the truth, all across the house there is not one degree of difference that we can measure or tell, with or without TRV's.

Still, I would install TRV's if I were you, to account for solar gains, internal gains or rooms where you have guests who refuse to leave.

Mike T., Swampeast MO

I've been trying for years to understand how the Vitodens 200 manages to quite closely maintain space temperature without sensing space temperature...

Even though I have a fully TRVd system (old gravity conversion with standing iron rads) with what I consider poor radiation balance, I've found a barely adequate heating curve that closely maintains space temp throughout the house. While I cannot measure actual flow either in the system as a whole--much less to individual radiators--I am nearly positive that the TRVs very close to wide-open in most cases.

I have feedback (public and private) from homeowners with the Vitodens 200 driving systems with cast iron radiation with NO form of thermostatic control and they report reasonable success. Imbalance problems [seem] to come solely from the sun itself. Sun bathed, south-facing rooms (often the formal rooms at the front) tend to overheat during the day while north-facing rooms (especially enclosed porches or add-ons) tend to underheat.

Wind (and BTW there is NO "wind chill" for a structure--only increased infiltration), snow on the roof and even occupancy gains [seem] to have little effect. It's the sun that causes "problems" and there's no reasonable way for any control system to compensate unless you use proportional flow control via FHVs (floor heat valves).

Presuming this is a new home of somewhat typical design:

1) I'd design the main-floor common spaces to operate SOLELY from the Vitodens control.

2) I'd use air temp modulatingFHVs (floor heat valves) in private spaces such as bedrooms and panel [floor] temp modulating FHV valves in baths.

In the scheme of a new house, such will add little to the cost, but if unacceptable, your only recourse is careful design of the heating panel (floor) with tube size and spacing suited to the load of the room. This alone could result more expense than using FHVs...

Rich Kontny_5

Wind Chill

The words right out of my mouth. If you are trying to heat the outdoors or a poorly insulated housing envelope with windows and doors open you may have to factor in wind chill.

Rich K.

Ron Gillen

It's Magic

I have to think that the Vitodens gets some sort of feedback from what's happening in the low loss header. I see no other way that it can maintain indoor tempuraure as acurately as it does. I have all infloor with Heatlink headers and thermostat wires to every room but haven't found a reason to install stats and zone valves. If they were installed I would still ride the curve and use the valve as a high limit in specific areas like a cooler bedroom.

dblagent007

No thermostats

My understanding is that the no thermostat system would be designed to have a valve for each zone. During the initial process of dialing in the heating curve, the flow to each zone would be adjusted with the valves to provide the necessary amount of heat. What this means is that the valve for the zone with the greatest load will be wide open and the rest will be closed to some degree. Once all of the valves have been set for each zone the Vitodens simply follows the heating curve and all of the zones stay at the same temperature.

As for thermostatic vavles in each room, I guess I don't really see much of a difference between that and having a thermostat in each zone. I guess the FHV could give me room by room control. However, my zones are pretty small so I feel like I already have that anyway.

From what I am reading, it sounds like a no thermostat system accounts for almost everything except solar gain. My home is new construction and we have installed the tinted windows with low-e coatings.

My current thinking is that I will run thermostat wires to all of the zones but still try the system out without any thermostats. If it works okay and we don't have too many problems from solar gain, then I may just leave it that way. If there are problems, then I will put in the thermostats and run it that way. Do any of you see any problems with this strategy?

The guy that I talked to about doing this strategy said that they do it all the time in Europe, but that in the U.S. everyone is so conditioned to use thermostats that very few people will take the chance.

Unknown

flow and temperature rise tells you heat loss.

The viessmann is measuring the heat loss through the boiler pump and temperature change at all times, I wager.

that said, I prefer the system to see what's going on in multiple zones. It's not "top of the line" if some solar gain throws it off, IMHO. That is, if comfort is the goal.

ALH_4

No Thermostats

I do not see any problem with giving it a shot. It may work great for your home. If there is a north facing room with three exposed walls and lots of windows it might not balance very well with the rest of the house.

It's all about diversity in the heat load from zone to zone. If the heat loads are close, this strategy will work fine. The temperature in certain rooms may not track exactly as it does in other rooms, but if you are willing to "tinker" with the flow to each zone, I think you can get the system balanced.

TRV's arent quite thermostats. Thermostats are on/off, TRV's provide an analog response to the indoor temperature. In effect, they provide continuously variable flow balancing just as you propose to do manually. Ideally, the TRV's would be just opening as the boiler comes out of warm weather shutdown, and you would have continuous circulation throughout the system.

If you are using the 6-24, you probably do not need the low loss header, depending on your heat loss.

Keep us posted. The Vitodens 200 is ideally suited to this type of system.

Maine Doug_66

No Thermostats

The apartment I built in my building, an old bank, has a radiant floor. About 19 yards of concrete with 6 zones, constant circ, VSI controlled by Tekmar with north wall outside sensors. No thermostats. The concrete is tinted and ground smooth so there is only one oriental carpet in the bedroom and a towel warmer as a zone in the bathroom.

The Tekmar has to be tweaked for fall and spring where the days can be warm and the nights very cold. The problem here is that the 3 am outside temp may be freezing but the daytemp may be 20 degrees or more warmer. The floor however has seen much hot water because the Tekmar does not know that it is spring or fall. So I have learned to tweak the curve untill winter sets in and then the floor gets very happy and runs by itself.

Since I am selling the building I am going to add a thermostat because people want thermostats. Maybe I just won't connect it to anything......

Uni R_2

Wind Chill Effects

In order to dial in my outdoor reset curve last winter I ran my Prestige for several weeks off of the outdoor sensor directly without the thermostat. The wind chill (more appropriately - increased infiltration) didn't affect things at all. This was using a boiler with a controller that doesn't have any smarts of its own and directly maps water temps to outdoor temps.

Like the others have said, solar is what you have to watch out for.