Viewstat with Heated Flooring

nickvda

Hi, I was wondering if the new color viewstats are compatible with Heated flooring, I know they are according to manual, but more of a question if anyone has done it. The heated floors in question are from Rehau http://www.rehau.co.uk/building.solutions/underfloor.heating/floor.systems/floor.systems.shtml. Anyone have worked with these? And if so how did you connect them.

Thank you!

vining

Typically with radiant floor heating you set it and forget and only occasionally make minor changes, a degree or two, or on/off at the beginning and end of the heating season. Unlike force hot air system radiant heating takes time to reach temperture since the water temperature flowing through the pipes is at best 110 degrees and you often run the floors by using slab temp sensors that keep the floor temp just slightly higher than the desired room temperature. In most cases the floors only run 72 degrees so you don't have rapid flucuations on the slab and in the air space.

Basically I wouldn't waist my money a slick T-Stat when a low profile room temp sensor (or invisible) and a cheap back room T-Stat is all you need since the user shouldn't interface with this anyway. Some systems I've done recently don't even have room (air) temp sensor and just use the slab sensor instead. When using the slab sensor the back room slab sensor T-Stat maintains the slab at 70-72 degrees which in turn keeps the room at that same temperature. In this case all I do is make or break the slab sensor from pulling in the circulator (mixing block) and boiler for seasonal changes or extended away periods. Only if you want to give the customer the ability to change the slab temperature a few degees would I bother with a communicating T-Stat.

DHawthorne

The only time I've communicated with radiant floor heaters has been a simple on/off. They aren't responsive enough to make anything else practical, unless that specific model is something radically different. Though I imagine a customer might like to know what temperature it was at even knowing they can't monkey with it much ... though it's kind of hard to mistake if they are running or not.

nickvda

I forgot to mention, the house will have air conditioning as well, so basically it would just have to make sure the floor is not trying to heat while the ac is blasting cold hair and so forth.

Thank you!

vining

nickvda wrote: »

I forgot to mention, the house will have air conditioning as well, so basically it would just have to make sure the floor is not trying to heat while the ac is blasting cold hair and so forth.

Thank you!

You'd be suprised how often that happens. Most people think when they have radiant floors that the floors will be all warm and cozy which it seldom is unless you're heating a small area and the central air system cover a larger area and draws the excess heat from room with the radiant and disperses that excess heat through the larger area. Otherwise the room temperature will be just slightly lower than the floor temeprature. If the room is kept at 70 then the slab will probably average around 70-72 degrees. Not warm and toasty toes at all unless you run both system, heating the floor while cooling the air which lasts for a while until someone tells them about the $$ they're spending runnig these competing systems. HVAC guys won't tell them since they just sold them on having toasty toes.

nickvda

Is there any way to coordinate both system with the viewstat, so as to reduce and minimize costs and conflicts as much as possible?

Thank you

vining

Just track the state of the floors zones and HVAC zones and write code as you see fit.

nickvda

Thank you for your answers Vining.

Your last post leads me back to my initial question, how do I go about connecting the heated floor system to the viewstat? Any experience with this?

Again thank you very much for your help!

vining

Normally I wouldn't use a T-Stat but relays to enable or disable the radiant systems control system similar to what Dave suggested but if you want to use the Viewstat you would typically connect to the RH & W terminals. Making sure the jumper that often goes between RH & RC (cooling) is removed so you can run seperate isolated systems.

This really depends on what controls the HVAC contractor is using since they will probably use slab sensors and an outdoor reset (temp) sensor and possibly room air temp sensor so you really got to know the a system and what's being installed. In your scenario I would probably use the viewstat as the primary room control in series with the radiant floor sensor control to allow the floor sensor controller to act a secondary limit for a "max" temperature allowed while the viewstat controls the desired temp but with out knowing all the parts and pieces it's hard to say how to wire it.

DHawthorne

vining wrote: »

Normally I wouldn't use a T-Stat but relays to enable or disable the radiant systems control system similar to what Dave suggested but if you want to use the Viewstat you would typically connect to the RH & W terminals. Making sure the jumper that often goes between RH & RC (cooling) is removed so you can run seperate isolated systems.

This really depends on what controls the HVAC contractor is using since they will probably use slab sensors and an outdoor reset (temp) sensor and possibly room air temp sensor so you really got to know the a system and what's being installed. In your scenario I would probably use the viewstat as the primary room control in series with the radiant floor sensor control to allow the floor sensor controller to act a secondary limit for a "max" temperature allowed while the viewstat controls the desired temp but with out knowing all the parts and pieces it's hard to say how to wire it.

That will work just fine with the older Viewstats, but the color Viewstats power off the RH terminal, and AMX won't support anything but using the furnace/air handler to power them. A zone valve won't do it, and chances are there's no common run to the stat in any case. That said, I just completed an installation with a bunch of them powering off an external supply, and using Aprilaire 8024 relay boards to isolate the outputs (which was a royal hassle, since AMX insists they need 2A each, which is insane for a thermostat). One of the stats smoked when the heating zone activated ... I'm convinced it was a bad stat, and a brand new one in the same location, same wiring, same power, works just fine; but AMX won't cover it under warranty, even though it was exactly 2 days old, because of my "unsupported" installation.

vining

DHawthorne wrote: »

but AMX won't cover it under warranty, even though it was exactly 2 days old, because of my "unsupported" installation.

if i recall to be compliant you have to completely re-wire the HVAC system's power to use the 2 amp supply required or use isolation relays between the t-stat and the hvac controls. Either method is ridiculous and illustrates what a poor design these deivices have. The isolation should occur on the t-stat and the t-stat power should be independant from then hvac control power.

I would imagine you'll have the sales guys spec these in all your future jobs.

DHawthorne

vining wrote: »

if i recall to be compliant you have to completely re-wire the HVAC system's power to use the 2 amp supply required or use isolation relays between the t-stat and the hvac controls. Either method is ridiculous and illustrates what a poor design these deivices have. The isolation should occur on the t-stat and the t-stat power should be independant from then hvac control power.

I would imagine you'll have the sales guys spec these in all your future jobs.

Actually, the won't even support it WITH the isolation relay. I can't tell you how many times a tech support person quoted the doc that says they *must* be powered off the HVAC unit. Logic, common sense, and science be damned, if you don't follow that instruction, your warranty is void.

vining

DHawthorne wrote: »

Actually, the won't even support it WITH the isolation relay. I can't tell you how many times a tech support person quoted the doc that says they *must* be powered off the HVAC unit. Logic, common sense, and science be damned, if you don't follow that instruction, your warranty is void.

Tha standard HVAC xformer is 40va/24v which is only 1.6666 amps so unless the installed equipment xformer is 48va or more your SOL. Seems the sensable thing to do would be to spec anything other then the AMX stats until AMX gets their act together and either re-designs the t-stats or amend the specs so they can be installed in typical installations with full warranty. Until then i won't use them, it ain't worth the aggravation.

ericmedley

Vining,
Interseting point above about customer expectations on heated floors. I always told clients not to put too much stock in it. I always said the floors won't be warm, they just won't be cold.

DHawthorne

vining wrote: »

Tha standard HVAC xformer is 40va/24v which is only 1.6666 amps so unless the installed equipment xformer is 48va or more your SOL. Seems the sensable thing to do would be to spec anything other then the AMX stats until AMX gets their act together and either re-designs the t-stats or amend the specs so they can be installed in typical installations with full warranty. Until then i won't use them, it ain't worth the aggravation.

Tech support blithely told me to upgrade the transformers in the air handlers ... which, granted, is not a big deal really, but I refuse to do it. My "unsupported" installation is working just fine, and I imagine many others are as well.