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Radiators more efficient the radiant floor?

But then again, who pays attention to the numbers?

As for the application, I would tend to agree. For example, a passive designed home. I would NOT recommend placing tube in the high mass slab. I'd prefer to go with either panel rads or radiant ceiling. Anything but radiant floors. Seen too many jobs where compounded solar/floor gain causes discomfort due to over temp.

The numbers I spoke of dictate 2 btu/sq ft per hour per degree difference in surface vs air temp for a floor, and 1.7 btu/sq ft /hr for a panel. But as I also said, who pays attention to the numbers but BTU geeks like me?

I think the key to ANY heating system is the ability to change emitter response quickly (low mass emitter) and follow the load precisely (non electric TRV's). But the emission system is only as good as the heat source and the distribution system, hence the need for indoor/oudoor reset on a mod con with a variable speed distribution pump. This way, the system can react quickly to changes and deliver only what is necessary to insure comfort.

Of course, eliminating human discomfort due to window loss has a lot to do with it as well...And when the window (low mass) can change its operating characteristics (emitting surface temps) quickly, then it is possible to deliver high quality comfort in a heart beat as well.

Nice to see you Ted. See you at the RPA?

ME (Watthead West)


  • Ted_5
    Ted_5 Member Posts: 272
    radiators more efficient then radiant floor, what do you think?

    I had a meeting with a radiator company out of Belgium last week. They are claiming higher annual efficiency over low temp radiant floor if you use their low temp radiators. Main reasons are, can set back more degrees with better set back recovery, spring and fall it is better for their low mass, low water volume radiators, takes less energy to heat up the space. Also, less chance of over shooting space temps. Has anyone else heard this before? What do you think?
    One thing I found very interesting is their test lab. It has two identical homes built side by side in a large build that can cool down to -35C, that is about -31F! There they can simulate these conditions and prove what they claim. I wish we could do this with boiler brand X against boiler brand V! Maybe someday? Any way check them out, they are coming soon to the US. http://www.jaga-usa.com/

  • Ted_5
    Ted_5 Member Posts: 272
    what about setback and recovery?

    Do you buy in to the government studies that say setback saves energy? I can see a scorched air system being setback saves energy, but not radiant floor. Maybe the use of radiators and doing setback would save energy?

    Nice to hear back from you Mark! How are thing looking for work in Colorado this year? Is the houseing market down there?

  • Doug_7
    Doug_7 Member Posts: 233
    It's the Time-Temperatue Factor

    The government information that thermostat setback will save energy is perfectly correct for your typical poorly insulated houses with low mass heating systems, such as forced air. Setback the thermostat, the house temperature drops fairly quickly - and at the lower temperature the house looses less heat due to the lower delta T saving money.

    The important factor in determining the benefit of setback is TIME.

    How fast does the house cool down and heat back up versus the available setback time? To get a cost savings benefit, the house has to be at the lower temperature for a reasonable number of hours.

    With a well insulated house with a high mass heating system, there is probably not enough time for the house to cool down in an overnight setback. But if you are away for a week or more, then setback will work great, because there is lots of time for the house to cool down - and the house looses a lot less heat due to the lower delta T.

    A well insulated house with a lower mass heating system, such as radiators, could provide more time for overnight setback to work. The radiators would need lots of area to run at the same low water temperature and high efficiency that floor heating does.

    In our building, which is well insulated with a fairly high mass floor heating system (PEX in Gypcrete) we tell owners not to use setback unless they will be away for a week or more. Some are away all winter, in which case deep setback saves a lot of money.

    So it is the Time-Temperatue Factor - or system dynamics that determing the benefit of thermostat setback. There is no one simple answer for all cases. The right answer is - that depends.


  • my BS meter goes off whenever someone talks about "water volume" and "energy usage" together.

    The two are very nearly completely separate issues. I see "Low H20" all over their website, yet water content would have nothing to do with efficiency. In fact, coupled with a mod/con boiler as they say, less water content would further exacerbate any cycling issues that might already be present.

    There are scenarios where I could see a radiator saving energy. Namely, improperly insulated floor systems driving additional downward losses, and improper use of setback on mass systems. Maybe a weak form of radiant vs low temp radiators. That's about it, I think. So while it's possible to design radiator systems that are superior to inferior or poorly operated floor systems, I don't think these particular radiators are specia

    That said, they are likely cheaper than a lot of radiant floor methods and make a great system for those projects that don't need or want to walk on their radiator. some nice looking radiators too.

    I am so tired of misleading marketing though.
  • hot_rod
    hot_rod Member Posts: 21,792
    depends on how they

    define efficiency, I suppose.

    Sounds like they are blending comfort with fuel utilitization, and system distribution efficiency?

    I would think it would be hard to compare systems like that that are very opposite. building usage and climate at the location could be a big factor.

    Frequent and wide outside temperature swings would seem to benefit low mass small water content.

    Consistent cold temperatures sure gets along well with radiant mass systems.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ted_5
    Ted_5 Member Posts: 272
    This company also had to

    do a study for the UK government to prove their rads are more efficient then most brands in Europe. They had two identical homes side by side in the UK, not in their test lab. The houses were empty, so they had to simulate people living there by emitting small amounts of BTU's via electric heat to simulate bodies and other internal gains. Also, they opened and close doors. Their study over all showed 10% fuel savings over the other brand of radiators. I thought that was a very impressive number! Here in the US we need more studies done like this one. Maybe someone should try to use these rads in the next solar decathlon? They were designed to be used in solar and geo applications.
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