Tag Archives: HVAC

Radiant Basement Floor

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Posted on May 30, 2015 by

Earth sheltered homes normally get very scaled down heating systems (some even skip them entirely).  Where I live, a heating system is required for occupancy, so rather than get an expensive furnace that I would hardly use, I decided to go with an inexpensive “on demand mini boiler” hot water radiant system.  I got quotes for install that were as high as $60,000, but figured I could do it for a small fraction of that, so I decided to pull my own mechanical permit and do this myself.  I read a couple books and planned it out.  Then I bought the manifolds and supplies from PexUniverse.com (less than 400$ for the basement).

We got it all installed and inspected (our first mechanical inspection) and then had Dysert Concrete handle the actual pour of the floor.

ExplainingTheSituation_40

 

Installing the radiant floor was easy, but some of the recordings didn’t work out, so the final video is shorter than usual.  You can read the story below for the details that wouldn’t fit in the narration.

The Video:

The Story:

I started with working out the layout on the computer.  Building code requires that no circuit be longer than 300 ft, and most experts recommend that you balance the lengths of the radiant tubes, so you definitely want to plan it out ahead of time.

I tried a number of different plans that ran the tubes thru the hall to the various rooms, but it was just too inefficient and cumbersome to get things “zoned” well that way.  In the end, I decided to drill some 5/8ths inch holes thru the base of the mechanical room wall to simplify the layout.  With the right tools (DeWalt hammer drill and a long 5/8ths inch bit), that was pretty easy.

We had leveled out the pea stone after the “underground inspection”, but David helped me do some final leveling of the peastone and then Zack helped get the 6 mil plastic down.  This plastic is important for keeping water vapor from the ground out of your concrete floor and is required by building code.  It also helps keep the radon out, etc.

Six MIL?

A mil is not a millimeter.  Six MIL is six thousands of an inch or roughly 0.152mm.  Before most English speaking countries switched from the imperial measurement system to metric, they would have called it a “thou”, based on the Germanic route word for “thousandth”, but for some reason, America decided to go “romantic” language based with this one and called it a “MIL” instead (based on the word for “thousandth” in languages like French or Italian).  This is a similar etymology to how the rest of the world got the word “milli” for the Metric system, hence the similarity.

HuskyWe don’t use “MIL” much in the USA, except for quantifying thin film thickness.

Since it is difficult to imagine things in thousands of an inch;

  • 1 MIL = grocery store bag
  • 2 MILS = Garbage Bag
  • 3 MILS = Husky Contractor Bag
  • 17 MILS = Pond Liner
  • 35 MILS = Credit Card

 

JigSaw Puzzle

David tossed us some sheets of insulation and we got started on the jigsaw puzzle.  My rooms are unusually shaped and since they didn’t actually stock those shapes at Home Depot, we cheated by cutting pieces.  We started with measuring, but usually ended up trimming each piece iteratively until it fit.  We taped all the pieces together and shoved trimmings into any gaps along the wall.  Not too hard, but certainly more time consuming than a square room might have been.  This probably wasted about 15$ worth of insulation, so not too bad.

Radiant tube

I marked the radiant tube layout directly o n the insulation based on that balanced plan I had carefully worked out on my computer.  I used piece of scrap wood marked with the right size increments and a can of upside down surveyors paint.  In addition to basic tic marks to follow, I also painted in the end loops so the whole plan would be pretty easy to follow.

Radiant_Layout_DrilledStapling the Pex tubes down was easy and fun, Sherri and I took care of most of it, but the boys were very eager to try it themselves.  I imagine it would have been quite a lot more difficult (and much less fun) without that commercial grade tool we used.  The tool cost quite a bit (~200$) but is very well built and I will use it a lot… I also plan to sell it and recoup most of the money at the end of the project anyway.

Radiant_Layout_Apse

 

Connecting the pex to the manifold was straightforward and easy.  There are some simple little brass connector bits and you just tighten a nut to hold it all together.

Manifold

Pex Stapler saved us a lot of timeI got the Manifold, Pex pipe, the Pex stapler, staples and the pressure tester from “PexUniverse.com”.  I had looked at lots of other sites (including sites that put it all together for you, such as Radiantcompany.com), but this one had the best prices and the best hardware.  There are also easy to find “coupon codes”.

John (my brother-in-law) and Zack helped me finish off the third loop.

My sister Bonnie was in town and mostly helped me with the ICFs (another post/video), but she made it into this video by helping me to fill the tubes with water so they wouldn’t float in the concrete. I had been trying to pour it from the bucket into the funnel, but she had the idea to siphon it from the bucket, which was much easier and didn’t get us as wet.

Then we pressurized the system (according to building code) so we would know if anyone punctured the pipe before the concrete set.

Concrete

Concrete day arrived and the guys started with putting down some six by six wire reinforcement.  This was left over from the garage floor and will help prevent cracks from growing.  It also helps protect the pipe and keep it all down under the concrete.

The concrete was pumped in from overhead (renting the pump truck cost ¼ of the job, but was well worth it in terms of making things go easier), and spread level.  They came back an hour later and hand troweled it smooth.

Concrete_AwYea

Costs

In all, I paid less than 1$/sft for the insulation, radiant tube, manifold and supplies, then 3$ for the concrete work plus an extra ~500$ for the pump truck and ~1100$ worth of concrete…  So, not bad.

 

I hope to get the “quad deck” in soon so we can put another concrete floor over this basement.

 

Heat delivery

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Posted on March 1, 2014 by

Contents
  1. Hydronic

(under construction)

Hydronic

I wanted hydronic heating, rather than forced air.  Hydronic is more efficient and more uniformly distributes the heat in a way that feels more comfortable.  Hydronic heating is quiet and you don’t feel drafts or blow dust around your house.  In a passive solar design, hydronic can potentially be used to store solar heat in the fluid and move it around to where it is needed.

Hyrdronic is more affordable during new construction than trying to retrofit for it later.  Functionally, it goes well with my concrete floors.

There are some down sides.  Without the furnace filter, dust simply settles to the floor and needs to be swept up.  Randiant functions by first heating up the slab, which then slowly radiates out to the living space.  The amount of mass involved adds a lot of inertia to the system, so it responds slowly to change.  Adding carpets or rugs or even hard wood floors increases the resistance between the heated mass and the living space, further slowing the response time.  Adding carpet could also increase the temperature of the slab, which can reduce the efficiency of the heat exchange with the hydronic fluid (heated water).   This is more pronounced in warmer areas where the hydronic temperature is set to 85F rather than in northern areas where it is typically set to 160F.

 

Earth Tubes as Part of a Home HVAC System

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Posted on November 27, 2012 by

Earth to Air Heat Exchangers (or Earth Tubes if you want to sound less scientific about it) are really only part of your home HVAC system.  In an ideal world, the Earth Tubes would heat/cool and dehumidify all the air you would need for your home via passive means.   In reality, you are going to need fans to augment the air flow and the air coming from your earth tubes is likely to need some additional dehumidification.  It may also be a good idea to mix it with “return” air as part of your whole home circulation.  You may want to add filters, heating/cooling coils, etc.  In some ways, the rest of the HVAC system would be like a normal home, but it could all be sized much smaller due to the advantages of drawing the intake air thru the earth tubes.

Here we explore some of the considerations and adjustments that may be needed when combining earth tubes with more traditional HVAC solutions.

 

Dehumidification

One of the main concerns about underground living is cool walls leading to condensation of humid air and, eventually, unhealthy mold.  Hot humid outside air drawn directly into an earth shelter will condense on the cool interior surfaces.  However, if the air is drawn in thru cool earth tubes, the condensation can happen there instead.  Of course, you don’t want mold in the earth tubes either, which is why you want them made out of nice smooth HDPE pipe and sloped to carry the water away.

If the temperature outside is a balmy 95°F with a Relative Humidity (RH) of 100% and it passes thru a 60°F tube, the cooler air can not hold as much moisture even as it maintains the same relative humidity.  Once it enters the home, it is mixed with other air and warms up to 70°F.  Since the temperature has now increased, the RH is only 70%, which is much better than outside, but still a bit high for comfort.   If the earth tube temperature was only 51°F and then the air was allowed to warm back up to 70°F, the RH would only be 50%.   This idea of dipping the temperature of the air as low as possible to force the water out of it, and then raising the temperature back up again is precisely why Air Conditioning (AC) units are so good at dehumidification.   They usually drop the entering air temperature well below the comfort level in order to force the moisture out of it before it enters the home and mixes with the “return air” to warm up again.   Note, these units do not attempt to cool and reheat all the air, only the entering air is cooled and it is then mixed with the warmer air that we are trying to cool.   When humidification is wanted without cooling, the evaporator and condenser are both placed in the flow.  The evaporator reduces the temperature of the air, condensation is drained off and then the condenser uses the heat it just removed upstream to warm the air right back up again.   This is all a lot easier if you dehumidify the air as it enters the home because you have less volume to worry about, so be sure to dehumidify before mixing with the return air that you are re-circulating thru your home.

 

Fans

Fans are needed to help move air around for ventilation or other reasons.  If you are using a forced air heat system, you will need larger fans to transport the heated air thru the home and then return much of it to the furnace to be “reheated” and used again.

Most forced air HVAC systems for above ground homes use 85% return air and only 15% fresh air.   I plan to use radiant floor heating, so my fan requirements will be significantly lower, my house will be quieter, less dusty, etc.

 

 

(more to come)