Recommended design water temperatures?

Ken_25

Reading an old Calgary Herald article,(date missing) were Dave Yates is quoted as saying "Energy savings generated by the system - proponents say it typically is 30%- is achieved by not having to heat the water any more than 85 to 95 degrees F."

Is there any sort of agreement or accepted practice for the design water temperature. Do you radiant guys really try to keep the design temps low.

Perhaps if Dave reads this he could clarify to me if perhaps the 85-95 would be a more average water temp and not a design day temp.

Thank You

Al Letellier_2

defign temp

The only accepted practice is to provide enough water temp to deliver the required BTU's to heat the space. It's the same as any heat delivery system. A good heatloss calculation, manually done or by computer will give you the required BTU. Then you pick the delivery system or installation type for radiant. It's not rocket science, it's just that radiant typically uses lower temperatures, and it depends on a lot of factors as to what the temperature will be.

S Ebels

No one recommended temp

The temp depends on a number of factors but the two that determine your final point are these. What is the load (how many btu's do you need at design) and what heat emitter are you using.

To simplify this, imagine a room load of 5000 btu. You could in theory, heat it with 1 foot of baseboard running at 600*. (purely hypothetical)

Or you could heat it with 10' of baseboard running at 180*.

Another option would be to size the baseboard or a panel rad to provide design heat at 140* by increasing the length of the BB or using a 24" x 36" rad for example.

Option three would be to run 85-95* water through the slab floor giving our 200 sq ft room an output of 25 btu's per sq ft.

Water temp is driven by the load and what you are using to put out the heat.

The heat emitter is dictated by the constraints or conditions of the job.

The lower the water temp, the more efficient the system becomes.

Put those facts all together and it's supposed to mean something coherent. Don't know if I accomplished that for you but hey, I tried.

Weezbo

Today the water temp is 60 degrees in my radiant floor....

been like that for a week now...so maybe theres something to low water temps ...it is constantly recirculating this temp...so maybe the temp of the water depends on what the amount of heat that is required to heat the room to a given temp is a way to say it...another stradgey would be to pump higher temp water andwatch the t stat drift up and down and pump intermittently 280 degree water into the system....it might cause system and component failures though...and if i like to be sweltering for a while to the point i could hardly breathe and freezin at some distant point in time it might work at even higher temps...

dconnors

Keep in mind that.......

Heat goes to cold. So the floor temp must be higher than the room temp in order to impart any heat to the room. A 60 degree floor will not make a room 70 degrees.

Weezbo

True .... Buh i didnt read where he stated he wanted it to be

70 degrees *~/:) The laws of physics apply here also :)he did ask about accepted designe though so i will forgive me my oversight

Ed Gutowski_2

The 30% energy saving claim would be hard to prove unless someone did a before and after test on a particular system. I have my doubts about this claim. I have heard the people will "feel comfortable" with radiant ceiling systems where the objects (people) are radiated and people say they are comfortable even though the air temperature is lower. This may result in less energy input to achieve "comfort" because you are not heating the air. I suspect it may work in some cases but not in all situations.

I think the above addresses your question however on the topic of water temperature: An ideal surface temperature would be about 80 in a residential living area or occupied office. What your floor is made of (wood or tile) will be a factor in your water temperature. The higher the resistance, say wood or carpet, the harder it will be for heat to flow from the hot pipe to the cooler room and therefore the temperature will need to be higher for a floor using products with a higher R value. If people complain about hot feet, you are to high.

Lobbies and other "pass through" areas can tolerate a higher surface temperature.

Good Luck

jerry scharf_3

MRT

Ed,

I can' comment about the 30%, but I can comment on your doubts about comfort with lower air temperature. There are 4 major things that go into human comfort relative to heat, air temperature, air motion, humidity and mean radiant temperature (MRT). If you increase the MRT of a room (which is what a radiant floor/wallceiling will do) you must lower the air temperature or the occupants will get uncomfortable. There is lots of research to back this up. The fact that radiant heating also tends to produce much less air motion, this also makes people feel warmer for the same air temperature.

The heat loss to the outside is based on the temperature and net R value (factoring in leaks, voids...) If the temperature of the surface goes up, which it will do for the radiant heat surface, that will lose more heat, the other surfaces will be cooler with the lower air temperature. You need to do the calcs to see if this is a win or a lose.

jerry

Ken_25

I guess I didn't explain my question very well. I keep reading or hearing claims about radiant being more efficient. It is all through the advertising and articles.

I have an article I picked up at a trade show booth . It reads "The water circulates at temperatures of 90 to 120 degrees. Heat is steady and gentle. Lowering operating temperatures means decreased fuel consumption; case studies show an average of 20% to 30% reduction in operating costs.

All this information seems to be telling me that if the system was designed to supply sufficient heat at 95 degrees rather than 130 degrees that it would be more efficient and thus cheaper to run.

My problem is understanding that if this lower temperature could be the design temp just by adding a little extra pipe, why is that not a desirable and or sought after result when you are designing these systems.

Perhaps I am reading the promotional information correctly , or is it that it is only for promotional purposes and not really based on any facts.

Arthur

floor temperature.

I guess what you are wanting to know why is it more efficent?
The greater the temperature differnce the greater the heat loss will be, So if the floor is run at 90deg it will lose less heat to the surroundings than if the floor was to be run at 130 deg, (ie heat loss from the perimeter or downwards rather than just into the room.
However to get the same heat into the room from a floor at 90 deg will require a greater floor area to be at 90 than if it was 130 deg. ie more pipe in the floor.
Of there comes a time when even if the maximum pipe is in the floor and room is not met then the floor temperature will need to rise.