Radiant Heat - Low Secondary Loop Temp

Brad White_9

Regardless of insulation, what kind of contact does the tubing have with the sub-floor? Is it just suspended in the airspace?

Without contact you are warming the cavity which in turn warms the floor. To do this takes much higher temperatures. Say you want an 80 degree floor and you have an intervening R-value of 2.0. Call this about 22 BTUH per SF for the radiant area.

Your average water temperature should be in the 113-115 range IF you have contact plates or a more direct contact between tubing and floor.

Without this contact, the cavity itself becomes an insulator, adding at least another R-1.0. Because it becomes the contacting medium, the air wants to be in the range of 134 degrees in rough terms to get the same BTU/SF output. Your water temperature will want to be in the range of take-your-pick depending on the amount of tubing and surface area it has.

But be certain, to heat air to 134 degrees takes water a significant range higher than that.

dkottke

I've got a question about my new radiant heating system. Its a between the joists over hardwood flooring installation in an old house. The radiant tubes have about 2 inches of dead space and are well insulated underneath (R-19 and Reflectix insulation.) It uses an injection pump control (Invensys BB3000 Series) to control the pump speed and boiler firing (System 2000).

I look on the BB3000 and see that the secondary loop setting is always at least 15 degrees higher than the secondary loop temperature. For example, the setting is now at 132. The boiler fired when the measured secondary temp was 99. The secondary loop temp went up to 115, after the boiler shutoff and will now drift back down. Is this normal?

My floors are never warm - only room temp. The heat can't hold temperature during cold weather. Last night we dropped 6 degrees in 12 hours as the temp went from 20 to -4 degrees F.

Any ideas?

jp_2

original installer?

what does the original installer say? they installed it, they should fix it.

got pictures of the piping?

dkottke

I've got a call into the original installer. I've suspected that there might be a problem, but it finally got cold enough to be sure.

I'll see what I can do about pictures.

dkottke

The installation uses a mix of aluminum heat transfer plates (along the outer walls) and clips (on the interior part). Imagine the outer four feet has the transfer plates, while the inside uses clips.

I get what you are saying about need for high temperature. I guess I'm wondering why the secondary loop sensor says the fluid is 15 - 30 degrees lower than the set point. The set point is 132 and the sensed temp is 100 - 115.

Brad White_9

Sensor versus Setpoint

Can you adjust your setpoint? Does the (EDIT: Injection) circulator have the range? I would hope so.

My suggestion is that you adjust the setpoint upward if you can. It may well not be balanced hence you are not meeting your target temperature.

It also may be the labelling of the controls, what you think is the radiant setpoint is really the boiler or something simple like that. It could also be sensor location if remote. Might it be hanging loose or without good contact?

Now, the boiler itself (not sure what kind) has a different and higher setpoint. Assuming it either has to protect itself from low temperatures or is serving other spaces requiring higher temperatures, this is entirely normal.

Your boiler setpoint would be a certain offset above your lower target temperature. This keeps the lower temperature controller in a range with "something to work against". (The opposite of this is that the boiler is the same temperature as the lower temperature zone and the lower temperature zone would take everything it could to the detriment of control and possibly other spaces.)

Weezbo

were you to have a variable speed injection system

that varied the water temp you might not have the difficulty ..is what Brad is saying. it changes flow and availabile water temps to the areas consequentialy the temps change. drastic temps changes outside another aspect comes into play ,Ramp time....i gotta run. consider what Brad is saying and see if you can dial the setpoint temp Up.

dkottke

I have a variable speed injection system

sorry, I wasn't more clear.

The BB3000 varies the pump speed, the secondary loop temp, based upon the outdoor temperature, the turn on of the boiler for its zone, etc.

There's a couple of parameters that are set during start up and then it auto-magically determines the secondary loop temp setting. The startup settings are near the top of their range. (Here's the link - its a kind of large PDF http://source.invensysibs.com/literature/pdfs/F-27030.pdf )

So what happens is the BB3000 picks a secondary loop setting and then measures the temp in the secondary loop. If the temp is too low, it turns the boiler on (System 2000). The problem is that the temperature in the secondary loop never gets close to the temp selected by the BB3000.

Right now, the pump speed is always at 100 percent. Its trying to deliver heat, but the temperature is too low, so it never gets to slow done.

Brad White_9

It is a great day when dear Weezbo

steps in to translate for me!

Thanks, Weez... I owe you!

As for the system at hand, I think your curve adjustment needs an upward tweaking, whatever it takes to raise the temperatures to your distribution. Be forwarned though, you may be trying to compensate for something that is beyond the capability of water temperatures, the floor contact issue.

Brad

dkottke

Water Temperature

Okay, I get where you are going. But let's imagine, I've got a perfect floor contact and the curve is properly adjusted. (I'm not saying this is the case or that its even possible to get perfect contact.)

As was pointed out, I need temperatures above 115 to heat the air-space properly - probably in the 130 - 135 range. I think the problem is that the water temperature never gets that high. It stays around 115 or less.

Either the mixing of water from the boiler in the storage tank isn't right, or there's way too much loss of heat through the system. I think the insulation should keep the heat loss down. So my guess is that the mixing is cutting off too soon and not heating the temperature in the secondary loop sufficiently.

Once I get the temperatures in the secondary loop closer to the desired set point, then I can look into the very valid points about contact with the floor and curve tweaking. But if the water never gets hot enough, it will never heat the floor, even with proper contact.

dkottke

Problem solved

> I've got a question about my new radiant heating

> system. Its a between the joists over hardwood

> flooring installation in an old house. The

> radiant tubes have about 2 inches of dead space

> and are well insulated underneath (R-19 and

> Reflectix insulation.) It uses an injection pump

> control (Invensys BB3000 Series) to control the

> pump speed and boiler firing (System 2000).

>

> I

> look on the BB3000 and see that the secondary

> loop setting is always at least 15 degrees higher

> than the secondary loop temperature. For example,

> the setting is now at 132. The boiler fired when

> the measured secondary temp was 99. The

> secondary loop temp went up to 115, after the

> boiler shutoff and will now drift back down. Is

> this normal?

>

> My floors are never warm - only

> room temp. The heat can't hold temperature

> during cold weather. Last night we dropped 6

> degrees in 12 hours as the temp went from 20 to

> -4 degrees F.

>

> Any ideas?



It turns out that the aquastat in the buffer tank was set to 115 degrees. So the boiler never pushed the temperature above that point, no matter what the secondary loop setpoint called for.

With the temperature in the buffer tank adjusted upwards, the secondary loop setpoint and the measured temp are much closer (and sometimes the same.)

The floors feel warmer and are warmer than the room ambient temp.