good points on the buffer tank, Doc.

You plan to use radiant everywhere in the house, correct? If so you don't need to worry about the air handler temps, since they will only be on in cooling.

That's what I'm thinking now. originally, I was thinking of using the upstairs fan coils for heating the second floor bedrooms. Trying to weigh out the benefits of each. since the rest of the house will be radiant, and I have to run pipe up to the FCUs anyhow, it might be just as easy to put radiant up there. Problem is, the subfloor will be exposed as the first floor ceiling (2 x 6" T&G) and was originally going to be the exposed second floor deck. To do radiant upstairs, I'll have to re-think that.

My original plan was as Chris copied above. I'm trying to sort out now, based on what I'm learning, what the most practical approach is going to be.

Also think about carpeting and how it effects the design (and temps). In some cases, I would use radiant internal walls (preferred) or ceilings.

If you use FC and low temp radiant, and use one buffer tank, your efficiency will go down, since the zone with the highest temp requirements will dictate the minimum buffer tank temperatures. Try to go the extra miles and put radiant on top of the subfloors with aluminum plates to keep the supply temperatures down.

I tell my customers that if they use carpet I will shy away from the project, since it is like wrapping your radiators in blankets to make sure the don't perform well. People live under the perception that carpet adds comfort, but they don't understand that the more they feel the warmth of the floors, the more comfort they add. A few area rags are usually OK if you are middle eastern origin and you cannot live without them.

Radiant walls are nice in the shower, and I yet have to see radiant ceiling to work well with low temp radiant. But you are talking about 10 btus/sqf heat load on average, very easy to achieve with 85F supply temp and top of the floor radiant.

We don't plan on putting carpet anywhere to my knowledge. the basement and mud room will be stamped and stained concrete slabs. The first floor will be either tile or hardwood depending on the room. The second floor is currently designed to be 2x6 tongue and v-groove, exposed top and bottom. I can look at doing a different second floor detail, but have to consider that with the timber frame, the exposed joists below are spaced at 2' 8". I guess it would be easy enough to add some thickness to the floor detail (maybe 1/2" plywood sleepers with wood flooring over that). Lots to consider.

As discussed in the radiant forum, no matter what you do, a single tank temperature is dictated by the highest load to radiator output ratio. Doesn't matter if it's because of fan coils, big windows, wood flooring or limited floor space to put tubes in. Balance is critical. A fan coil and radiant in a room needs less temp (heating mode) than radiant alone.

Posted By jonr on 07 May 2013 04:08 PM
As discussed in the radiant forum, no matter what you do, a single tank temperature is dictated by the highest load to radiator output ratio. Doesn't matter if it's because of fan coils, big windows, wood flooring or limited floor space to put tubes in. Balance is critical. A fan coil and radiant in a room needs less temp (heating mode) than radiant alone.

The point was if Danreed considers using fancoil only for space conditioning (without radiant), he has to be aware of the fact fact that fancoils do not deliver any meaningful BTUs with supply temps less than 100F, thus having FC and radiant zones on one buffer tank, the higher needed temps for the FCs will dictate minimum buffer tank temp and will not allow to run the radiant floors at 85F, thus impacting efficiency very negatively....wether it is discussed in the radiant forum or not.
An who would want low temp radiant and FC operating together, having uncomfortable 75F air blowing into the room?

There is enough griping about 85-90*F air supplied by heatpumps...

I can't imagine trying to heat using air blown across a coil supplied with 85*F water.

Excellent. I only lost a little bit of sleep figuring out how to get radiant onto the second floor. Done! Let's move forward.

Radiant floor heating, fan coil cooling... undisclosed capacity heat pump unit (to preserve the peace), and XXgallon buffer tank (with the option of a second to accomodate Mrs 76's +/- 4 degree tolerance for temperature swings) Ducted ERV for outside air exchange. Single circulating pump (variable speed, constant pressure) zone valves for radiant zones and FCUs.

Now the question becomes... is it going to take some kind of super-computer to run such a system? I wouldn't think so, but I defer to the professionals on this one.

I mentioned the Tekmar 406 earlier. Without a comprehensive control you can do a hard wire switch from heating to cooling season, however with the 406 you can explore radiant cooling as well.

Joe, we tried to use the 406 and it failed to do certain aspects for the job outlined in WEL0664, where it was supposed to do everything.

http://welserver.com/WEL0664/

Have you used the 406 and did it do what it was supposed to do? I did not find a good application for it again, but I am anxious to try.
Dan, the answer is no, no computer, if you stick with radiant heating and FC cooling, the controls are fairly simple. How many people in your household for DHW?

4 total in the household (normal days).

Doc I'm installing a 406 now. How did it fail you?
We have an Emerson Einstein 2 on a 25 ton system that did not dissappoint, but it is much more expensive.

I believe when I wanted to run different zone at different temperatures and needed to prioritize on them (DHW) with a 3 way Belimo valve I could not get the 406 to work for me. Maybe I was inpatient and did not dig long enough into it, and ripped it out and did it the old fashion way with a couple of relays. If you keep it simple, heating zones all one temp, cooling all one temp, I am sure it works like a charm. But that is not our typical application, because we run hot water 24/7 off the same heatpump, something Dan here might want to entertain if he has 4 people in the household, each one of them probably using more hot water than he does. Each one of my daughters regularly manage to drain a 108 gallon tank down!

he has 4 people in the household, each one of them probably using more hot water than he does

yep. they think of our current "demand" electric water heater like a big feller does an all-you-can-eat buffet... it's a challenge to see who can kill it!

hey doc... check yer messages when you get a chance.