basement too hot
Last Post 05 Dec 2014 08:40 AM by sailawayrb. 32 Replies.
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BlogloUser is Offline
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21 Nov 2014 03:16 PM
After extensive renovations, we have a new concrete slab for the basement with a 4 zones radiant system and a polished concrete floor. the problem is that the air get too hot in the basement. Even if the controller stop the boiler and close all zoning valve when air reaching 70deg, the remaining heat in the slab keep heating the air until 77-78. (exterior temp around freezing point) if i keep the temps to 66, the air temp is ok but the slab is not as comfortable and feel cold. all thermostat sensors are working ok. no other heating sources. 5 inch slab over 2.5 inch rigid styrofoam, 900 sqf,4 zones, honeywell controller and thermostats (setted at AF - air-floor sensor) and 7.5 kw boiler set to 120F. how to achieve a comfortable floor temp and a comfortable air temp at the same time ? thanks guys
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21 Nov 2014 05:32 PM
Slabs overshoot the setpoint temperature unless controlled with a thermostat designed to deal with the much larger time-constants/thermal-lag. What are you using for a thermostat on the slab zone?
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22 Nov 2014 12:14 PM
You must have the outdoor reset feature if you want perfect comfort in a low-load building heated with a radiant slab, this is especially true of basement remodels.

Your radiant floor designer should have specified the proper controls and given you the design water temperature for your project, which is likely bit over ambient and not going to give you the toasted toe feel you anticipated. Still, comfort is the absence of discomfort.
MA<br>www.badgerboilerservice.com
sailawayrbUser is Offline
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22 Nov 2014 07:15 PM
What Dana said, namely you need the right thermostat for controlling HR concrete slabs that provides the required control anticipation. If your thermostat doesn’t have slab temp feedback, you have the wrong thermostat. Sometimes clueless designers will neglect to specify slab temp control feedback. Sometimes, clueless installers will neglect to connect the slab temp sensors to the thermostat. So make sure that you have the right thermostat, carefully read the thermostat directions to make sure that you have properly connected all the temp feedback sensors (i.e., indoor, outdoor, and slab temps), and make sure that you have properly programmed the thermostat too.

Outdoor reset just modulates the supply temp as a function of outdoor temp and does nothing to prevent the indoor temp overshooting that you are experiencing.

If you have a low-load energy efficient building, your floor surface temp may only be a couple degrees above the indoor temp set point and your supply temp may only be in the mid 80Fs. A floor surface temp of 72F doesn’t provide the warm barefoot feeling that you might be desiring/expecting, however, it shouldn’t feel cold either. If you have a high-load energy inefficient building or a bad HR floor emitter design, add 5-15F to the aforementioned floor surface temp (which will provide a warm barefoot feeling) and add 15-45F to the aforementioned supply temp...and budget a lot more for your heating bills...

Congrats on the polished concrete floor. That’s the best and our favorite way to finish a HR concrete slab, especially if you have a low-load energy efficient building.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
jonrUser is Offline
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22 Nov 2014 11:19 PM
Outdoor reset limits the supply temperature and therefor the btu delivery rate and therefor the overshoot. Do use a thermostat that makes use of outdoor temperature.
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23 Nov 2014 10:24 AM
Outdoor temp feedback and associated supply temp reset should be used along with indoor temp and slab temp feedback as previously stated. However, it is the slab temp feedback that eliminates indoor temp overshoot and undershoot if you have a thermostat that is using all this feedback. Only the slab time/temp variation has the knowledge (i.e., the slab thermal lag time characteristics) that the thermostat needs to generate the required anticipation to allow maintaining the desired indoor temp without overshoot and undershoot. Outdoor temp reset by itself does nothing to eliminate indoor temp overshoot and undershoot.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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23 Nov 2014 11:38 AM
5 inch slab over 2.5 inch rigid styrofoam
Wondering what the purpose of the 5" slab was. Thinner slabs should not only reduce the overshooting issues, but improve response times too.
I suspect the high supply temperature has some contribution to the overshoot as well. Right now I'm using all air-sense thermostats over the slabs with a supply temp of 85F and we aren't noticing any overshooting, despite some fairly big changes in outdoor temperature.
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23 Nov 2014 12:56 PM
There won't be much of a difference between 5" versus standard 4" HR concrete slabs with regard to the thermal lag time characteristics. You are precisely correct that outdoor temp reset becomes less important with increasing low-load energy efficient buildings. Obviously, the less influence that the outdoor temp has on the indoor temp because of having better insulated and sealed buildings, the less becomes the benefit of outdoor reset...but you still should use it. However, you should always use slab temp control feedback with concrete slab HR emitters to avoid indoor temp overshoot and undershoot.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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23 Nov 2014 01:28 PM
You can't control overshoot on any radiant slab without outdoor reset. You can use slab and ambient temperature stats but they are of little use in a basement without the added challenge of solar gain.

Experience with renovation and new construction has saved our customers thousands in unnecessary controls.

We use ambient thermostats in 95% of our radiant work, both new and old with the same results as ICF reports.
MA<br>www.badgerboilerservice.com
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23 Nov 2014 05:07 PM
Controls are likely the lowest cost component in a hydronic radiant floor heating system…and likely the most important component for comfort too. So while designer/installer competence is often an issue here, cost should not be an issue at all.

I wouldn’t expect solar heat gain to be a significant factor in a basement, but if it is, than you will likely need a better overall solution and a better control capability than a standard residential thermostat can provide even with full indoor, outdoor and slab temp control feedback. ICF and I discussed and beat that horse to near death already:

Dealing with Significant Passive Solar Heat Gain

We use PLCs for our integrated Passive Solar and Hydronic Radiant heating system designs. We have designed/installed some pretty sophisticated industrial grade PLC systems for less than what some companies sell/install standard residential thermostats:

PLCs

For new construction where a slab will be poured, a concrete slab hydronic radiant floor heating system has the lowest acquisition cost compared to any other heating option, is the most energy efficient hydronic radiant floor emitter that can be currently designed, and is by far the most comfortable heating option. If one also needs air conditioning and absolutely wants to minimize operational cost, than mini splits start looking real good.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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23 Nov 2014 11:14 PM
I'm still trying to figure out this radiant slab/passive solar thing because we just don't have a problem with it. When we have a cold snap which means temps down at design temps (about 20F or so for us), it became clear that the supply temp needed to be increased. I manually bumped up the supply temperature from 85F to 87F or 88F trying to get a feel for how I was going to program the outdoor reset in the future. That seemed to take care of it. Sometime later, I installed all the door handles during a cold snap and it immediately became much warmer inside, so I put the supply temp back to 85F, which seemed to take care of it.

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24 Nov 2014 07:52 AM
I am with ICF.

You can get fancy-- no one gets fancier in residential radiant floors than Uponor with their Climate Control Network System-- but you probably don't need it unless your house qualifies for hotel status.

As for a specified slab not costing anything extra, dah.

Here in Minneapolis we design, install and repair hydronic radiant slab-on-ground, suspended slabs, suspended floors from below and above with dry and wet (gypcrete), radiant wall and radiant ceilings. They all provide perfect comfort if properly applied.

In basement remodels, which we do several times a year, we admonish our clients to forego offsetting, overheating fireplaces, plasma TV's and other sources of heat that may idle their radiant slabs and give them that cold concrete feel.

MA<br>www.badgerboilerservice.com
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24 Nov 2014 08:25 AM
ICF, your home is both low-load energy efficient and benefits from considerable passive solar heating. During the recent PNW cold snap the weather remained mostly sunny...and it is November such that your passive solar fenestration should not have received significant roof overhang shading. So presumably you received considerable passive solar heat gain during this recent PNW cold snap.

So this recent PNW cold snap is likely a situation where you would NOT want to bump up the HR system supply temp (i.e., what outdoor temp reset would normally do) because the passive solar heat gain would more than compensate for the slightly increased heat loss that resulted during this cold snap given your low-load energy efficient home. In fact, this could be a situation where you would want to reduce the HR system supply temp in the zones receiving passive solar heat gain (i.e., just the opposite of what outdoor temp reset would do).

Bumping up the supply temp (i.e., either manually, via outdoor temp reset, or by using a smarter control algorithm) would be more appropriate for the situation where you have a cold snap, but you do NOT have significant passive solar heat gain. In this situation, the HR heating system needs to make up for your slightly increased heat loss.

I am not sure how changing the door handles had an impact unless you are saying that this caused you to have the exterior doors open during the cold snap for some period of time. If so, are you saying that this event caused the indoor temp to increase...immediately or sometime subsequent? I would have expected the indoor temp to immediately decrease, which could then result in the HR system increasing the slab temp (depending on the control algorithm being used), which would then result in increased HR system heat gain, which could then result in an indoor temp overshoot after the doors were closed (again, depending on the control algorithm being used). Are you using slab temp control feedback?
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
BlogloUser is Offline
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24 Nov 2014 09:48 AM
the thermostat are honeywell AQ1000TN2 with both air sensor and floor sensor setted to "AF" (air + floor)

found out that 2 sensors at the water input and water output of the boiler were not installed. The installer said that my boiler is only on/off, so these sensors were not necessary. but in the honeywell manual, it said to install them whatever type of boiler your have. now the floor is not overheating.

I wonder how these sensors have an impact on the controller. I think that the controller use these values to determine the amount of heat stored in the slab by calculating the temp difference between the send/return of the water. If the water come back hot, the slab has enough energy stored.

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24 Nov 2014 11:47 AM
Good deal Bloglo! Yes, your description of the return/supply temp feedback is precisely how we address passive solar heat gain effect on a zone-by-zone basis with our PLC based control algorithm in lieu of using outdoor temp reset because of the previously described issues associated with using outdoor reset if you have a passive solar heating system. This approach better addresses what is actually driving the slab temp (e.g., increased slab heat loss because of colder outdoor temp or increased slab heat gain because of passive solar heating). And closing the control loop using slab temp feedback in addition to indoor temp prevents overshooting and undershooting.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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24 Nov 2014 08:06 PM
During the recent PNW cold snap the weather remained mostly sunny.
It was awesome :-)

So this recent PNW cold snap is likely a situation where you would NOT want to bump up the HR system supply temp
Good point. I am hoping that the heat loss from the door hardware openings was enough that I will be able to keep the supply temp low and not turn on outdoor reset. Or, maybe set it really low so I don't have to deal with it. In those really cold streaks, we usually run a wood fire 24/7 anyway.

Oh, sorry, without the door hardware in all the doors had holes in them and you could feel the outdoor air jetting in. The multipoint locks closed tightly enough, but there were still those little holes in them for the spindle and keyway.  The standard doors had big round holes in them for the lock and deadbolt and they were held shut with a dowel, but that didn't seal them very well.  When I installed the hardware, I took extra care to seal it all up. The wind can be blowing 15-25 outside and an ICF home is now like a tomb inside. :-)
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24 Nov 2014 08:19 PM
You can get fancy
I recently had the occasion to see a number of million and a half dollar homes which were victims of the original recession. The heating systems never worked despite having cost upwards of $100,000. The bank was getting ready to sell them and the HVAC nerd was going through them muttering while he ripped out the fanciest control systems I had ever seen. I'll bet there was $15,000-$20,000 in some of them.
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01 Dec 2014 08:48 AM
Room-by-room feedback is fine but unnecessary in most residential design. When sizing large rooms with 50% glass facing the sky slope such systems are really ideal. But my experience has been like ICF's. Most are not knowledgeable enough to design, install or service such systems so is a disfavor to design them where they are not appropriate.

Outdoor reset with boiler driven boost works well on nearly all residential hydronic systems, from hundred year old cast iron to radiant ceilings in a new sun room addition and since it is standard equipment on all high efficiency condensing boilers we use is on nearly every design we do.
MA<br>www.badgerboilerservice.com
sailawayrbUser is Offline
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01 Dec 2014 09:07 AM
Outdoor temp reset does NOT work in low-load, energy efficient buildings that have significant passive solar heat gain for the previous reasons clearly explained. Outdoor temp reset was a crude way of improving hydronic system performance in high-load, energy inefficient buildings back in the old days when boilers were primarily used for heating…and for this, it works well. It is certainly true that the majority of HVAC contractors these days don’t understand this and also don’t even understand when a simple control approach is more than adequate or when a more sophisticated control approach is required.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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01 Dec 2014 10:09 AM
I suggest that large radiators, OR and well insulated buildings (ie, low radiator temps) put a natural cap on the overheating issues that can be caused by high mass radiators. If a slab is heating a building when only 75F, it's a sure thing that it won't be transferring heat into the room when the room overheats to or past 75F due to solar gain.
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