Radiant heat in very low energy homes

Edmeister

I haven't taken the time to read through all the posts but here's how we avoid that complaint. It's not 100% (what is?) but these rarely fail to avoid the issue you're talking about.

Use a system that resets it's water temp according to outside air. Bang bang control setups are poor for radiant heat and the higher the mass the worse they are at maintaining comfort.

Don't tube the whole floor. We'll typically run tube along the first 2-3 feet of the perimeter, then concentrate on the areas that will see traffic. Under furniture areas, cabinets, area rugs are prime candidates to skip.

Run as low a water temp as possible. In some of these places, 80* water will do the trick on a mild winter day. A floor that's heated to a 73* surface temp is still better than a floor sitting at 65-68*.

Explain the fact that the floor will not be "warm" all the time going in to the job. It helps dispell the false notion the the "toasty toe" ads promote. This alone will eliminate 90% of the headaches with "cold floor syndrome".

Basement floors aren't as warm with with the baseboard upstairs because previously you were heating the entire house via the basement! Now that you've removed the upstairs load, the basement floors no longer need to be as warm.

from the archives...

I pulled this out of the archives...enjoy.
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The Inefficiencies in Delivery Efficiencies
Copyright ©2004, Robert Bean, All rights reserved
For HPAC Magazine
Approx. 1500 words
Nov./Dec. Issue

The man in the front row asked, “what would the design floor surface temperature be for a radiant heated home if the thermal load was less than seven Btu/hr/sf…”
In unison the rest of the room made up of heating contractors and wholesalers snickered, “seven Btu’s’ ya right!” (It was as if they had rehearsed the night before.) But they didn’t know sharing the next three days of a certification course was an award winning home builder recognized by both provincial and federal governments in energy efficient construction…I didn’t either until we had a private dinner that night and a robust discussion on building mechanical interfaces…but at that very moment here in the front of the class was a experienced contractor which had my attention because the answer to his question in a round about way was the radiant heated floor would actually feel cool to the occupant. Heated floors, which feel cool….not possible you say….well in fact yes it is possible and it challenges all who fail to understand the relationship between building efficiency and mechanical efficiency. The inefficient home under design condition requires floor surface temperatures of sufficient levels to compensate for the losses of the building. Fortunately for us comfort fanatics, at least at the moment, the building load in standard construction in relative terms to efficient construction practices translates to floor temperatures above our bodies normal skin surface temperature which is a nominal 84 ºF. However, the efficient home requires floor temperatures below our skin temperature, which means no matter what our logic struggles to understand, the body sensors connected to our thalamus tells us the floors are cool even though we have heated them. So while we raise our eyebrows in contempt and contemplation, we should be thinking about the perils of selling warmfloors when in fact in energy efficient homes warm floors they will not be. The dinner with the very bright builder was very much like a shortened version of some building efficiency courses taken a few decades back…a time period when we saw the birth of the R-2000 program, air-to-air heat exchangers and an embryo of a radiant floor heating business. So you can imagine the price of oil at 51 bucks-a-barrel entered our dialogue that night as did the shortened payback periods for new building technologies such as insulated concrete forms. When our exchange turned to mechanical efficiency, it became very interesting because not only had my colleague across the table mastered the art of efficient building construction he was acutely aware of the inefficiencies in delivering mechanical efficiencies – a topic I have studied now for a few years. It was at this point of our conversation I decided to stand down and let him paint the same picture created in Natural Capitalism by Hawking/Lovins of the Rocky Mountain Institute. An industry where 40% of billed time to the client is wasted waiting for someone to do something else. Where fuel and transportation costs are out of proportion to the products value. The same business, which inefficiently mines iron ore, copper, and coal and consumes tremendous amounts of power and fuel to make components and systems. In between our appetizers and first round of microbrews the builder itemized the entire inefficient process of creating mechanical efficiency, the alpha – omega, cradle to grave as it is often called...right down to the last litre of gas burnt to take products to the recycler or dump. Here is a short expose of his observations of inefficient processes consuming fuel and power to deliver mechanical efficiency…

“Robert, consider the fuel and power consumption in mining of raw materials such as the hydrocarbons used for transportation and manufacturing fuels or plastics or assembly processes (welding, soldering), and the minerals for feedstock (lead, coal, iron, copper, zinc), then we must consider manufacturing of feedstock for plastics, bar stock for valves, cast iron for circulators, air separators, and boilers, steel for tanks, furnace and boiler jackets etc…plus component manufacturing processes including machining, casting, forming etc…and how about the fuel consumed in consolidation of offsite manufactured components, plus power consumption for fabrication, and assembly processes for finished goods. Think about the transportation from manufacturing into the distribution network either to export terminals or central warehousing then the uploading from terminals onto ships. How about the environmental cost of ocean traffic for offshore products from Europe, Asia, or the Middle East typically via cargo ships. Then there’s the offloading at destination ports and delivery to import facilities plus the movement from import facilities or central warehouses to regional warehouses and onto regional warehouses and branch locations. Don’t forget the fuel consumed from branch locations to job sites and the permanent cycle of man and materials traveling from tradespersons residence to wholesaler to job site to home again. Finally and ultimately there is the gas and fumes to haul the dead stuff from the clients home to a recycle or waste facility…When we tally it up are we really any further ahead- are energy efficient mechanical systems really that efficient in the big picture?”

When he had just about exhausted the endless exploration of it all I stepped in asking for his solutions…he scribbled a few numbers and words on a napkin and slid it across the table…7 Btu/hr/sf and integrated systems…hmm was all I could muster. Then it hit me…in his own way he was pointing to prefabricated homes or at least prefabricated housing modules or sub systems like Dow Chemicals STYROFOAM™ T-MASS™ Technology. …he couldn’t change the fact that trees don’t grow into homes but he could change how homes are made from trees or concrete and steel. Furthermore, he understood that the inefficiencies in delivering efficiencies were too big for one man to change but he could control how much inefficiency he would allow in his clients home. Towards what I thought was to be the end of the evening, I asked him how long he had been living and practicing his housing philosophies… “my whole life”, he said….and I sincerely had to ask, “didn’t the local industry ever question your sanity”, his reply, “up until last year, I, along with a few other zealots were considered less than normal…the lunatic fringe so to speak”… “but in this part of the world oil is battling gas to hold onto market share and one would think the price would go down but world prices keep going up despite the competition. All the while, the hydroelectric producers are rubbing their hands because they know getting natural gas into an oil-dominated market is a major hurdle in shifting consumers minds while environmentalists along with insurance companies mix with heating oil producers much like water blending with oil. They also know increases in building efficiency make even the smallest oil boiler or furnace grossly oversized leaving very little choice but electricity in home heating.” At this point, Mr. Builder insisted we visit the boiler vs. water heater debate, which made me realize this was going to be a long night not because he wanted to take sides, but he genuinely wanted help trying to find a suitable method of delivering health, wellness, and comfort in a building which had virtually no thermal load. As the night went on, we discussed how his highly efficient buildings had greater than normal mean radiant temperatures resulting in a reduction in radiant losses from the human body and thus improved comfort without adding a radiant system. The economics he explained, to reduce the thermal load to nothing were not there so here ‘he and the fringe’ were stuck between “finance and violence” ie: kicking out the windows to create a load or finding a reasonable way of adding an almost insignificant amount of heat to the building during peak loads. Having a fair amount of experience in district energy systems I though for a moment about the benefits of consolidating thermal loads from a variety of buildings onto a central plant and it made sense at least at some cerebral level that in the presence of rising building efficiency there is in fact a need for mechanical efficiency but only when numerous independent loads can be collected at a highly efficient mechanical plant. In other words, on stand-alone projects, the greater the building efficiency the less need for mechanical efficiency, but in the presence of many insignificant loads there are possibilities for using a combo system comprising of not a hot water heater connected to a fan/coil or a radiant floor system but a fan/coil or radiant system connected to a great big water heater called – (drum roll please) a district energy system. This would solve a number of issues for this builder’s developers and oil companies facing competitive pressure from gas and electrical utilities. Furthermore any development designed around district energy and highly efficient buildings takes advantage of greater fluid delta t’s more so than traditional plants, simply because in relation to other district systems, all other things being equal, the plant could operate either at condensing temperatures for most of the year or could use slightly more aggressive delta t’s in the distribution network. No matter how one looks at it, the plant would be extremely efficient much like the community connected to it. Explaining this to my new student brought once again the reward of sharing knowledge as his enthusiasm grew at the thought of integrating district energy and energy efficient buildings. At that point the certification course on radiant hydronic systems seemed like a moot point…he’d find a way to reduce the output area of the radiant system thus driving up the floor temperatures…maybe use radiant walls instead…didn’t really matter at this junction as a new idea had been sparked which could potentially address the inefficiencies in delivering efficiencies.

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A comment: In 1998 we challenged contractors to ask what would have to happen for the building industry to make h/ac as we know it today – obsolete - then we released the above article in 2004 after spending some time studying embodied energy the rebirth of "exergy" as a useful tool fueled by the words from Hawking/Lovins (Thanks HotRod)...in the past few years we have seen a rebirth of an old topic – net zero buildings. I don’t what will happen over the next decade but I do know what industry considers to be the norm in electromechanical conditioning of occupants and spaces will change and the business person owing a HVAC firm should take a hard look at ones business plan… you'll know when you are stretching by the feeling of pain as you try to apply old ideas to developing challenges like eliminating 400 lbs of CO2 emissions per week per van/truck just by changing what you’re willing to defend.

Back when...

Back when gas prices first took a leap a few years back I got a lot of calls from people who wanted a high efficiency furnace installed to offset their fuel bill. I've always been customer rather than profit driven so I told them all "spend your money on insulation and windows", you'll save more money that way. I was never one to sell "a bill of goods".

Where is our industry heading? Net zero buildings? CO2 emmissions from my truck? (Sorry I'm not gonna walk or ride my bike to the jobs though I have in the past...really) Reducing heat loss to under 10/ft is an admirable start for any builder. I'm glad this thread took this turn because I agree with NRTRob, quit bitching that your floors aren't warm and bask in the knowledge that your heating system and envelope are doing their thing.

I imagine that some kitchens today probably can be heated with the Sub-Zero fridge they got cranking away in there. Add to that the 20 can lights that throw the same light as a few 100 watt bulbs. I think we all see where The Bean is going here. And it's a good way to go.

Ground source heat pumps. Zoned AC with chillers rather than DX. Radiant cooling. Pretty complicated stuff for a residence. My customers might be able to heat their house with a light bulb but I know their not gonna give up their AC. This comforts me.

This is a great thread. TG

BTW: The district heating thing was pretty cool. It would have to be a co-op or whoever ran it would eventually rape the users in our capitalistic culture. Add a wind farm and some methane recovery from the "town farm" and you got that town from "The Postman" movie with some perks.
Woo Hoo

I agree with Andy

For very low energy use homes I also like panel radiators with TRVs set up on a homerun distribution system. S/R each panel with 3/8" or 1/2" barrier PEX or PEX-AL-PEX. "Upsize" the panels a bit to get supply temperatures down and keep a condensing boiiler at high efficiency. You also get fast, room-by-room response to handle solar or other internal heat gains, which can be a real issue in such homes. Another advantage is that a single small variable speed distribution circulator (think brushless DC) can handle the entire distribution system on a fraction of the electrical energy usage of a blower in a FA system. It's not just about thermal efficiency.

Soundsa Nice!

I only dream of jobs with such forward thinking clients. I think you did absolutely right in designing the radiant distribution around the DHW load. Mix your floor temps down as low as possible. Since it's slab on grade, passive solar, and you looped it intelligently, valve down the solar gain portion of the floor and use the "shaded' loops for added heat. Surface temps will rise from longer run times as well as higher circ temps. They mave save a few fuel dollars if you switch to a modcon, but the setup you have now is fine. How much will they save since the house is so tight already. You can change the heating plant any time in the future.

Food for thought:

In passive solar homes should we go with radiant walls or cielings so as to not "preheat" the slab with our fuel $$?

Does radiant cooling operate more efficiently than forced air, or is the savings in the reduction of duct sizing to handle only the latent load.

TG

great thread

This thread reminds me of why I love the Wall

as far as habits, your right that some cultures are different.

Growing up we never wore outside shoes in the house unless it was a special occasion. Every Greek family I ever knew was the same way. I think that this is the same for a lot of Europeans. Come to think of it, I think that the U.S. is the only place I know where it is customary to just wear outside shoes inside. As for Greeks, (or any immigrants) I think after the first generation there is some assimilation and we don't always do the same thing as our parents, especially for those who marry outside of their parents culture.

I think it comes down to personal preference more than anything.

As far as radiant panel heating, we should sell on efficiency, and the fact that the whole house is comfortable. Minimal hot/cold spots compared to FA, or even baseboard convectors, and radiators.

Comfort boys, comfort

rb, your posts are excellent as usual.


Cosmo

We still have work to do

Goes to show you with all the Condensing boilers, 3 speed circs, tekmar controls, PAP tubing and all the other latest and greatest, the hydronics and sub category radiant heat industry is still far away from effectively selling comfort and efficiency. We ourselves have differnent ideas of what comfort is, and why should'nt we, we are
all differnt right. And in my opinion we try to blur this fact with images of babies laying on floors, and logos of happy toes. knowing we really cant deliver that always.
And so the radiant sector has companies that sell online to the DIYer, other home owners think they can save a few bucks and do some of the work themselves,( you almost never see a homeowner trying to bang some ductwork together ) and plumbers and even builders trying to jump aboard with little knowledge and training. Heat load calcs, we don't need no stinkin heat load calcs. I'll take a 1000' feet of 3/4 pex please. All because we don't have our stuff toghether.
A force air job or even some hydro air seems much simpler to the building owner furnace,duct,registers and a single t-stat. While we go in after , and try to sell pieces of parts, some hi tech,and another "radiant expert" tries to sell more pieces and parts, for good money and we say btw the floors may not be warm. Looked a lot easier on TOH.
So does it matter whats better, orange boilers or blue, staple up or down, outddoor rest or indoor reset ,oh look another condensing boiler just came out on the market I'll think I give that a try this week .
Know wonder we only have 7% of the market share in the u.s . What are they doing different in europe, is it the fancy controls they could slap on the wall, is it comfort, is it warm floors??? What is it I really like to know?
We are are own worse enemy, and its hurting the industry. I believe we need unified packages, good ,better, best. A unified voice total efficiency and comfort. I say again TOTAL efficiency and comfort. And hydronics is a better choice to deliver that because...Now let's talk about IAQ. Let's talk about building envelope.
Let's stop trying to sell WARM FLOORS.

Sorry for the rant guys.
Great topic, .... is any body listening?


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RFH

We are finding that the largest benefit in UFH with low energy homes is that the heat can be supplied using solar panels with a small electric back-up. Many of our customers also coil pipe in the ceiling as well as the floor to provide cooling in the summer (when using a heat pump chiller) . The customer requirement is mainly for highest comfort with the cost being less of an issue.
Regards
Simon

Warm floors

Wow, what a great thread this is!!!
Lots of great contributions and no personal attacks.
A definite "keeper".
Thanks for all of your great contributions.

Rollie Peck

Homeowner