Need some hydronic schooling

[TCaldwell]

This cold weather brought out some short comings, espically in our living room. A few years ago I upgraded the single element baseboard foot for foot with dual element baseboard, this really helped. The living room is 400sqft with probably more glass than it should with vaulted ceilings.
The basement is heated to 65 and the floor joist bays are workable, the living room floor is 2-1/4 wide x 3/4 thick strip oak with 3/4 thick by 6 inch wide diagonal tongue and groove subfloor. I understand this isn’t the best situation for staple up radiant but I’m interested in relatively low temp supplemental heat, to augment the higher temp baseboard. This is the largest room in the house, so basically I’d like to shift some of the load to lower temp heat rather than turn up the outdoor reset curve reducing useable storage. I’m looking for about 6000 btu out of the 400 sqft, hopefully with 125 deg water. The way the basement is set up I could use two 300 ft runs of 8 inches on center of 1/2 inch pex, would the headloss be too much for a 20 deg delta using a Grundfos 15-55 alpha circ or would I be better using 5/8 pex? Any thoughts would be appreciated

 

[__dan]

If there's no ceiling fan, installing one and mixing the air will make a huge difference. If the existing convection rads are big enough, next I might look at some control change. Ceiling fan is probably necessary.

 

[TCaldwell]

Two ceiling fans and control through Tekmar already, curious if others have done this and to what results, also math for above.

 

[peakbagger]

IMHO if you are going to spend money, spend it on reducing the heat loss out the windows. Heat loss calculators do not take into account localized cold spots from areas with large glass windows on room comfort.Double cellular blinds with side tracks will cut the heat loss way down and also reduce the radiant heat loss. The far less expensive but far more work method is to build custom "plugs out of isoboard and cover them with fabric, then put them in at night and take them out in the morning. If you really want to leave the windows uncovered in cold weather radiant in the floor isnt really going to do much. Think through how radiant heating and cooling works, heat flows from a warmer emitter to colder body via line of sight, unfortunately while the warm floor may keep your feet warm the windows are probably far colder so eat is going flow from your warm body directly out the window. You would really have to put in a lot or radiant tubing and crank up the temperature to make much of difference.

 

[nhtreehouse]

Any room for panel rads under the windows? I've got a similar situation in my living room - a lot of glass and my sub floors are even worse than yours. Mine are full 2x6 on the thin edge, plus 1/2 ply on top. 2" of sub floor with the same finish floor as you have on top. I was thinking of doing some form of radiant floor, but it would be a lot of work. I would have to demo the finish floor to get in there, then use some board product with channels routed out for the piping.

I'm also going to pursue peakbagger's route. There is a fabric product called "Warm Windows", which is a quilted blind material. They claim something like R6-7 over a single pane glass window. Never tried it, but seems like an interesting solution. Just before this last cold snap, I bought a couple of XPS boards and made blinds out of them for a unused room. Helped a LOT. with the loss from that room. Storage is an issue, but there is a bed in that room and I'll store them under the bed when not in use.

I have on order a 400mm x 3000mm panel rad to fit under the roughly 10' wide glass windows in my living room. I'll let you know how it works when I figure it out myself.

There is a phenomenon called the cold 70. Dan Holohan talks about this in his books. You room could be 70 degrees, but when you stand next to a large glass window, you are literally radiating heat to the glass and thus to the outside world. I believe that one reason why we put rads under windows is to introduce a convective airstream to effectively block the radiational cooling of the humans to the windows.

I'll work on the math next...

 

[TCaldwell]

Thanks Chris, I’ll look into the window coverings, however the other half probably won’t like. The double element baseboards are under the widows, that helps. I’m really only looking to this as supplemental heat that uses low water temp and thought radiant might be a thought, it would be controlled by a Tekmar 553 thermostat that stages two heat sources in the same room.

 

[pbvermont]

If doing radiant tubing under wood floor and want to use lowest supply water temperature, it is mandatory that you use the aluminum contact plates.
And best NOT to use the aluminum flashing gauge material. Use plates like Uponor supplies.

 

[JohnDolz]

Thanks Chris, I’ll look into the window coverings, however the other half probably won’t like. The double element baseboards are under the widows, that helps. I’m really only looking to this as supplemental heat that uses low water temp and thought radiant might be a thought, it would be controlled by a Tekmar 553 thermostat that stages two heat sources in the same room.

I agree with your other half. We put 2 big windows in our family room, fought with the installer to go absolutely as big as possible. We have cellular blinds in the rest of the house but refuse to use up the top few inches of visual with blinds. It may not make the best "economic" sense but that is some of the luxury we get by heating with wood.

 

[nhtreehouse]

I'll work on the math next...

Ok, the math...

Using siggy's formula (page 222), assuming 100 degree water (worst case, head loss goes down as temp goes up) the hydraulic resistance of a single piece of 1/2" PEX which is 300 feet long is: 12.29.

The equivalent hydraulic resistance of two parallel pex tubes is:

Req = [(1/12.29)^0.5714 + (1/12.29)^0.5714]^-1.75

Req = 3.65

Head Loss is Req*(Flow Rate)^1.75

I think you are going to want at least 1 GPM per tube, so that is 2 GPM total.

Head Loss(feet) = 3.65*2^1.75

Head Loss(feet) = 12.3 feet

From the pump curve for a 15-58, it looks like speed 2 will give you slightly higher flow rate at that head loss.

I also checked the uponor table and the head loss for 100 feet of 1/2" PEX at 1GPM at 100 degree water is 3.47. Three hundred feet would be 10.41, which is a little more optimistic than the math predicts.

All theory and no practice, so maybe someone with some experience will chime in.

 

[peakbagger]

Thanks Chris, I’ll look into the window coverings, however the other half probably won’t like. The double element baseboards are under the widows, that helps. I’m really only looking to this as supplemental heat that uses low water temp and thought radiant might be a thought, it would be controlled by a Tekmar 553 thermostat that stages two heat sources in the same room.

The window quilts do tend to be a visual distraction but are effective. The head bar of the cellular blinds is about 1 inch high and when pulled up the bottom bar and the blinds add up to 2". Most people have curtains in front of windows for privacy and these remove the need for curtainThe depth is of the head unit is about 1-1/4" which usually allows it to be in side the casing (to use the side tracks they have to be) Most visitors wouldn't even notice them. The major benefit is comfort, I can sit next to a window even in the coldest weather and not get a chill. They do transmit an opaque light on a sunny day unless they are ordered with a blackout option (used for home theaters and bedrooms).

 

[Fred61]

If your thermostat is satisfied or the temperature is at normal comfort levels and you still feel discomfort it's likely radiation coming off the windows. Many rooms that fit your description have similar problems. I had one. Way back before a boiler came into my life, I was heating with a stove and during weather like we have had recently it would not quite keep up.

The windows were on the south side (luckily) so we got good solar gain but when the sun set those windows would suck the heat from your body. I installed "WINDOW QUILT" which is no longer available and the difference was like night and day .The construction was simply a piece of thin polyester lining and a sheet of reflective mylar sandwiched between nylon decorative sheets of fabric.

This is where I spent most of my leisure time (except for when I had my head stuck in the refrigerator) and it was easy to feel the heat being sucked out of my body when the sun set.. Just lowering those shades made it instantly feel like the temperature in the room was raised by at least 2 degrees.

In my present home I have a mud room that has three outside walls and lots of glass. Unlike the rest of the house, the radiant floor runs nearly continuously. It's great to walk in there and feel the warm floor and instantly feel the warm ankles that just about make your whole body warm but I don't think I would move my recliner in there to read the paper.

 

[TCaldwell]

So Chris if I’m understanding your math then the headloss would be approx 12.5 ft at 1 gal/ minute per 300 leg of 1/2 inch pex , would the headloss be doubled if you have 2 , 300 ft circuits?

 

[DaveBP]

If you have access to the subfloor between the joists from the basement side, then adding radiant would give you some help. Siegenthaler could give you the numbers. But in the realm of human sensation and perception I'm never sure that numbers are a guarantee of satisfaction. Some of the pros here might have some useful rules of thumb.

The 300' loops could be broken into more and shorter runs with manifolds to reduce the added head.

Heat spreader plates would help tremendously. The extruded ones are probably best (if the finances allow) but these are easier on the budget and might be adequate, especially the double channel ones which are thicker aluminum.

http://www.blueridgecompany.com/radiant/hydronic/316/rht-heat-transfer-plates

Other than the subfloor radiant, the only other thing I can think of to put that lower temp return water to use would be a monster air handler, ductwork and some floor registers.

Felt house boots and a sweater, anyone?

 

[salecker]

We have quad pane windows up here and they are awesome.
-40C or F they remain clear with no frost,and you don't get cold standing next to them.
I would be trying some blinds or get better windows,you may destroy your floor putting heat under it.

 

[Bad LP]

In my own case cellular blinds do help where we have installed them but they are pricey. My wife is a quilter so window quilts could be an easy fix. The next project I'm working on is panel radiators to replace the BB. I've got the space for them and they won't look out of place in the house because it has a bit of contemporary design in it. I'd love Runtal BB but with the cost for that stuff it better be able to at least cook me dinner and open a beer or 3.

I have a pair of CI radiators that is going into "man town" but I'm a little uneasy putting them on an interior wall as 2 of the exterior walls are all glass.

 

[nhtreehouse]

So Chris if I’m understanding your math then the headloss would be approx 12.5 ft at 1 gal/ minute per 300 leg of 1/2 inch pex , would the headloss be doubled if you have 2 , 300 ft circuits?

Only if you put the two loops in series! (I was assuming parallel connections using a manifold)

My background is EE, can't spell GEEK without it. So I look at head loss as an electrical circuit and then have to remind me the exponents are not 1 anymore. I believe the head loss is going to be set by the longest parallel branch of piping. But you have to consult the pump curve to determine how much flow you will get at that head loss.

If the pump curve was perfectly flat, it wouldn't matter - you could continue to add parallel branches and get the flow you require.

Difficult to express in words... Make sense?

 

[heaterman]

Plates under the floor will be mandatory with that much wood between the tube and surface Tom.
Bare tube won't drive a lot of btu's through that without running nuclear type water temps.

We've used heavy plates from Hydronic Alternatives in MA. with excellent results. They use a C shaped tube channel instead of the typical upside down U. Seems to hold better on the end of a joist bay where you loop back. Less expensive than Wirsbo or Viega plates.