Radiant Slab Operation Costs

[d_douce36]

Hey Guys,

So just got my hydro bill after running my new radiant system in the garage for the first time, which was 2000Kwh higher then normal. The Garage is 28x32 with 10' walls and a 12x32' attic space in the 8/12 trusses. So all together 1280sqft of heated space. Walls are 2x6 with R22 roxul, ceiling with no living area above are R40+ and attic portion knee walls are R30 with the ceiling R22. The slab uses 2" Halo Subterra XPS graphite infused insulation across the whole slab. 2 foot Frost wings were also installed. Whole building is well sealed with 10 mill poly. Two 8x9 Cloplay R18 over head doors on the main floor. The attic space aboce has two 48"x64" triple pane low-e windows. The hydronic set up is a 9kw Thermolec utilizing 4 loops of 1/2" pex average runs about 200' at 14" spacing. The building is drawing around 66Kwh Per day at indoor temp of 14c or 57F with an average temp of -4c or 24.8F. Im in Manitoba, Canada and we will see temps down to -22F or -30c so the system hasn't really been tested. Boiler has supply temp of 120F with a flow rate of .3 Gpm on the 4 loops

My question to you guys is why is it costing me so much to run? What am i missing? Any suggestions

 

[86turbodsl]

Were the edges of the slab insulated? Not just under, but contact on edges too.

 

[bzinsky]

Well, you're using on average about 2750 watts continuously, or 9,377 btu's, or basically 2 space heaters, sounds about right if you ask me.

Hopefully you realize you can't capitalize on the any of the efficiency gains you get from a radiant slab using electric. The efficiency advantage you gain from a radiant slab is pretty much solely due to the fact that the water temp can be very low compared to other hydronic systems, low water temps = great at absorbing heat from a heat exchanger. An electric setup has the same efficiency regardless if it's an expensive hydronic system on a couple hair dryers hanging off the ceiling.

You could always rent a thermal imaging camera to see if you have any leaks. It works great for that. Home depot rents them now.

 

[bzinsky]

You know what you could do, is grab a couple $20 space heaters, run them on the 1500 watt setting for a few days, turn off the hydronic and see where your thermostat is at.

If it's much warmer than what you have it set at, you know you have a problem with your hydronic setup. I guess that sort of depends on the outside temp though.

 

[d_douce36]

Were the edges of the slab insulated? Not just under, but contact on edges too.

yep all edges as well as under the thickened edge where done

 

[Shop Specialties]

The first time you fire it up it takes a while to get everything up to temp. I would wait another month and see where you are at. Do you know what your return water temps are ?

 

[Tracs]

Hey Guys,

So just got my hydro bill after running my new radiant system in the garage for the first time, which was 2000Kwh higher then normal. The Garage is 28x32 with 10' walls and a 12x32' attic space in the 8/12 trusses. So all together 1280sqft of heated space. Walls are 2x6 with R22 roxul, ceiling with no living area above are R40+ and attic portion knee walls are R30 with the ceiling R22. The slab uses 2" Halo Subterra XPS graphite infused insulation across the whole slab. 2 foot Frost wings were also installed. Whole building is well sealed with 10 mill poly. Two 8x9 Cloplay R18 over head doors on the main floor. The attic space aboce has two 48"x64" triple pane low-e windows. The hydronic set up is a 9kw Thermolec utilizing 4 loops of 1/2" pex average runs about 200' at 14" spacing. The building is drawing around 66Kwh Per day at indoor temp of 14c or 57F with an average temp of -4c or 24.8F. Im in Manitoba, Canada and we will see temps down to -22F or -30c so the system hasn't really been tested. Boiler has supply temp of 120F with a flow rate of .3 Gpm on the 4 loops

My question to you guys is why is it costing me so much to run? What am i missing? Any suggestions

24x30 in Brandon, MB. Keep my garage at 16.6C or 62F 24/7. 6kw with 3 loops. No frost wings or under thickened edge insulation. About $150 a month to run it. My calculations are is it runs 12 out of 24 hours.

 

[Shop Specialties]

I just looked up your electric rates and looks like you are paying $.08 per kw. So you only paid roughly $160 to fire it up the first time, heat it 24/7 @ 57* with an average outside temp of 24*. I think that is pretty good.

 

[Thumper68]

What was the floor temp when you first fired it up? It takes a lot of energy to get the slab up to temp, once there the energy consumption goes down a lot.

 

[Jackfre]

It is kind of you to post your temps in centigrade and then, recognizing who you are dealing with, provide we gringos the farenheit numbers as well. Generally, we aren't smart enough to use metric.

 

[d_douce36]

The first time you fire it up it takes a while to get everything up to temp. I would wait another month and see where you are at. Do you know what your return water temps are ?

I don't unfortunately i didnt opt for the rehu with the return temp sensor. What indicator would the return temp be telling you?

 

[d_douce36]

It is kind of you to post your temps in centigrade and then, recognizing who you are dealing with, provide we gringos the farenheit numbers as well. Generally, we aren't smart enough to use metric.

Haha "gringos" i just know theres alot of guys with a ton of knowledge from all over and wanted to speak there language

24x30 in Brandon, MB. Keep my garage at 16.6C or 62F 24/7. 6kw with 3 loops. No frost wings or under thickened edge insulation. About $150 a month to run it. My calculations are is it runs 12 out of 24 hours.

Awesome yea im just in winnipeg. Sounds more and more like these Kwh consumptions are inline. Iv been mulling over the idea of doing a heat pump to supplement some heating BTU's in a more energy efficient manner, plus gets me some AC in the summer.