Opinions wanted on outbuilding/house mech. systems

[mjncad]

The economy may suck right now; but I still need to think about designing the future home on our 35-acres. I don't want to do the temporary mobile home routine; therefore the plan is to put up the outbuilding first to act as a field office, shop and materials storage building. I plan to have a bathroom with a shower, and a mechanical/electrical room in addition to the office. I'd like to get some opinions on what I'm thinking of doing out there.

The shop area would be heated with natural gas fired radiant heaters hung from the roof structure.

I'm planning on using a tankless water heater for the outbuilding's hot water needs.

The mechanical/electrical room would house the pressure tank and any water treatment equipment I may need for the well water. I am thinking of sizing the pressure tank and treatment equipment to serve the outbuilding and the house so as not to buy two of everything. The downsides that present themselves immediately would be potential adverse pressure drop from the outbuilding to the house, water volume issues, larger equipment may cost more than two smaller units (one for the outbuilding and one for the house); and the mechanical/electrical room and bathroom need to be minimally heated for freeze protection. However, these rooms will need heat since there will be water there anyway. Also, an alarm and/or monitoring system going to the house may be required to alert me to any problems since I doubt I'll be in the outbuilding everyday once the house is done.

Also I'm still figuring out what would be an energy efficient way to heat and cool the office, bathroom and mechanical/electrical rooms.

I was thinking of using in-floor radiant heating/cooling; but have pretty much decided against that for the shop area as I want to be able to drill holes in the concrete to mount power tools if need be. Yes, I could make sure I do an accurate as-built drawing, and the PEX tubing could be wire traced for electronic detection; but this seems more trouble than itï½´s worth.

The county doesn't require residential fire suppression systems; but I also have thought about a cistern to store potable water and do double duty as a firewater storage tank. This would entail more pumps; but could give the well pump more rest than the traditional well to pump to pressure tank system. Then again replacing or repairing a tired well pump may be less money overall than using a cistern based system.

Any thoughts, opinions, etc are most appreciated.

Thanks,

[jimbrown]

The shop area would be heated with natural gas fired radiant heaters hung from the roof structure.
<font color="blue"> Agree</font color>

I'm planning on using a tankless water heater for the outbuilding's hot water needs.

<font color="blue"> Agree </font color>


The mechanical/electrical room would house the pressure tank and any water treatment equipment I may need for the well water. I am thinking of sizing the pressure tank and treatment equipment to serve the outbuilding and the house so as not to buy two of everything. The downsides that present themselves immediately would be potential adverse pressure drop from the outbuilding to the house, water volume issues, larger equipment may cost more than two smaller units (one for the outbuilding and one for the house);
<font color="blue"> Size it for both. Pipe is cheap you can run 1/12 or even 2 in pipe to the house the drop will be minimal. </font color>

<font color="blue"> </font color>
and the mechanical/electrical room and bathroom need to be minimally heated for freeze protection. However, these rooms will need heat since there will be water there anyway. Also, an alarm and/or monitoring system going to the house may be required to alert me to any problems since I doubt I'll be in the outbuilding everyday once the house is done.

Also I'm still figuring out what would be an energy efficient way to heat and cool the office, bathroom and mechanical/electrical rooms.
<font color="blue">Small gas furnace/heat pump. You might not even need it if the radiant heaters keep the whole thing warm.</font color>


I was thinking of using in-floor radiant heating/cooling; but have pretty much decided against that for the shop area as I want to be able to drill holes in the concrete to mount power tools if need be. Yes, I could make sure I do an accurate as-built drawing, and the PEX tubing could be wire traced for electronic detection; but this seems more trouble than itï½´s worth.
<font color="blue">Don't like floor heat in shop area Unless it is maybe solar.</font color>

The county doesn't require residential fire suppression systems; but I also have thought about a cistern to store potable water and do double duty as a firewater storage tank. This would entail more pumps; but could give the well pump more rest than the traditional well to pump to pressure tank system. Then again replacing or repairing a tired well pump may be less money overall than using a cistern based system.

Proably over kill and I doubt that you could put out any kind of real fire.

[mjncad]

Jim:

Thanks for the quick reply! I tend to agree with you about the cistern and fire suppression system; but I thought I'd throw it out there for opinions. I forgot to mention in my original post that the volunteer fire department's fire house is about 2 - 3 miles away.

[jml755]

mjncad,
First question I'd ask is: Can you put up an outbuilding (accessory structure) without a primary residence? Here in Michigan, most townships/cities (with zoning ordinances) won't allow it. They'll give you a permit for BOTH the house and outbuilding and let you put up the outbuilding first as long as you start the house within 6 months or so.

Also, in a lot of places here, accessory structures cannot have any sanitary facilities. Utilities like gas, electric &amp; water are ok, but no toilets. Idea is to keep people from using the outbuildings as guest houses, inlaw apts, etc. Not sure why any of that is bad, but I've argued till I'm blue in the face with township building depts and planning commissions and gotten nowhere. If I had it to do over again, I'd look for an area without zoning ordinances so I could do what I wanted w/o big brother (government) looking over my shoulder.

If you've checked all this out already, sounds like you have a good well thought-out plan.

[mjncad]

I checked with the county zoning department and they have no problem with what I want to do. Their only stipulations were no kitchens and bedrooms. Since the office won't have a closet, it's not a bedroom.

The county actually like this idea better as its one less mobile home dotting the landscape that people have a hard time getting rid of.

My current county on the other hand had a fit when I asked about an outbuilding with a bathroom. That's why we made sure when we purchased the land it was not in the current county that we live in.

No matter where I live, I always try to find a home in unincorporated parts of the county.

Gummint is the biggest hindrance to entrepreneurship in the USA.

[Pat]

I have met several people who built their shop first to serve as temporary living quarters while building the house and letting the shop become THE SHOP. Three of these are still living in the shop from 3-15 years later.

I advise against any non vented gas heaters (not legal in many states.) Use at least a "B" vent and preferably direct vent. I have never heard a complaint regarding the comfort and efficiency of a properly installed and engineered in-slab heating system EXCEPT when used in an intermittently occupied space such as a shop. You don't heat a space on the spur of the moment with in-slab heat. Thermal lags dictate that you essentially have to heat it 24-7. Set back is not an appropriate strategy for in-slab heat. My Wirsbo T'stats for each zone of the in-slab heat have no setback capability. Each zone has two stats, one for the slab heat and the other for forced air (does have sophisticated programing including set back.) I set the air stat a couple degrees below the radiant stat so normally the hot air never runs BUT if there is lots of comings and goings at say a party or whatever and the room gets cooled more than the couple degrees below the radiant set point the hot air comes on till the temp gets back above the setpoint of the air stat.

Lets say you turned the T'stat down for the week end in your shop. It will be quite a while before the temp drops significantly and in the mean time the delta T inside to outside will drive a heat loss. By the time the slab begins to cool appreciatively (or maybe sooner depending on your specific extant conditions) it is time to turn the heat back on because you need several hours to bring it back up to the required number of degrees above your air temp setpoint in order for it to "shed" the required number of Btu's to accomodate the delta T inside to outside and maintain your space's indoor air temp (where the T'stat is located.)

That is not to say you can't reasonably use hydronics in an intermittently occupied space. I have some hydronically heated radiant ceilings (and radiant walls too but walls can pose a problem in a house due to picture hanging and such.). The thermal mass of sheetrock is relatively low so the lag is way less than in-slab. Radiant ceilings would work well in the office or any space with ceiling heights not very out of proportion to floor area. In spaces where the floor space is large then taller ceilings can be accommodated with radiant ceilings. Short ceilings, like 7 ft or less, will not be very satisfactory due to the hot head-cold feet issue. 8-10 ft ceilings work well. My ceilings in the areas with hydronically heated ceilings are 9 ft high.

It is all about radiant environment. Every thing in the universe radiates heat energy toward every other thing in the universe. When you walk up to a picture window in the winter and suddenly feel cooler, like there was a cold draft or something that is because your body is radiating IR out the window but the cold outdoors is not radiating much energy back to you so there is a sudden net loss. This deficit is perceived as that part of the room being colder even though a thermometer may say it is the same temp. Away from the window our body is receiving IR from the walls, floor, and ceiling as you radiate to the walls, floor, and ceiling. The net gain or loss is perceived as being in a warm or cool place.

Another thing about radiant heating. You will still probably end up with duct work for forced air for cooling since radiant cooling is even less well understood by HVAC practitioners than heating. You can't just pump cool water through the floor to lower the average radiant temperature in the space so you radiate out heat to the floor and feel cool like leaning against a concrete wall and feeling cool. It is altogether likely that the temps you would have to chill the floor to would be below the dew point and the floor would constantly "sweat" like the side of an Ice tea glass, not altogether wonderful for a carpet of even good footing on a slab floor.

Radiant cooling does work and is a wonderful thing when properly engineered and realized. Properly accomplished it dehumidifies and cools but is still often supplemented with an air handler and chilling coils.

An accurate as-built set of drawings/photographs of the in-floor slab pex installation is not an issue. The thermal time constant is the issue. It takes a long time to bring the slab up to temp and a long time for it to cool. It is NOT EFFICIENT because you will waste much more of the heat than you use.

Another respondent mentioned solar. I'll not comment on the economics of a solar installation as there are just too many variables to allow adequate coverage of the topic in this post BUT once you are using solar energy to heat the floor it may be less important to you that such a large percentage of the heat is wasted in your absence. I considered a solar collector with thermo-siphon water "pumping" (cheap to build and cheap to operate) but decided against it and rely on my geothermal water to water heat pump (and two other high SEER air to air units) to handle my house (5000 + with 3 attached shops adding another 2300 sqft.) I am considering sharing a waste oil and or wood fired heater between my wood working shop (about 800 sqft) and the newly converted space (tractor shed to metal working/welding shop ( a tad over 1000 sq ft) just because I may want to. The new metal working shop (21x48ft) shares 24 ft of common wall with the wood working shop and extending the ducting for heat and air from the wood to metal shop is trivial (and some non trivial electric dampers and control electronics to zone it.)

Overhead gas fired radiant heat has a very rapid response time and recovers quickly from an "airing out." It is used to good effect in hangars and garages where large doors are frequently opened. The warmed air may escape but much of the comfort is provided by IR radiation and that works with the doors open and the space quickly recovers after the door(s) return to the closed position. Overhead radiant requires little or no advance notice because the radiant heat virtually instantly makes the space feel comfortable.

I was at the cattle auction today (selling 5 weaned steers at about 500 lbs each) and there were two large hydraulically operated doors, one to let stock into the sale ring and another to let them exit. The doors were opening over and over as each animal/group came through, yet, I had to take of my hat and coat and unzip the legs of my insulated bibs to not overheat due to overhead radiant heaters. They heat the objects in the room (people included) not just the air. Like a warm sun on a cold windy day.

Pat

[mjncad]

Pat:

Thanks for the detailed reply. Please see my interspersed comments in your discussion.

Matt

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I have met several people who built their shop first to serve as temporary living quarters while building the house and letting the shop become THE SHOP. Three of these are still living in the shop from 3-15 years later. <font color="red"> I doubt my wife will allow this to happen. </font color>

I advise against any non vented gas heaters (not legal in many states.) Use at least a "B" vent and preferably direct vent. I have never heard a complaint regarding the comfort and efficiency of a properly installed and engineered in-slab heating system EXCEPT when used in an intermittently occupied space such as a shop. You don't heat a space on the spur of the moment with in-slab heat. Thermal lags dictate that you essentially have to heat it 24-7. Set back is not an appropriate strategy for in-slab heat. My Wirsbo T'stats for each zone of the in-slab heat have no setback capability. Each zone has two stats, one for the slab heat and the other for forced air (does have sophisticated programing including set back.) I set the air stat a couple degrees below the radiant stat so normally the hot air never runs BUT if there is lots of comings and goings at say a party or whatever and the room gets cooled more than the couple degrees below the radiant set point the hot air comes on till the temp gets back above the setpoint of the air stat. <font color="red"> The radiant heaters I plan to use are the sealed combustion vented to atmosphere type like one sees at Home Despot and other places. From what I am learning about in-floor radiant heat is that the trend is to get away from in-slab due to the reasons you have mentioned concerning response time. Also, in-slab in a house requires more structure to deal with a gypcrete floor above a basement or 1st floor.</font color>

Lets say you turned the T'stat down for the week end in your shop. It will be quite a while before the temp drops significantly and in the mean time the delta T inside to outside will drive a heat loss. By the time the slab begins to cool appreciatively (or maybe sooner depending on your specific extant conditions) it is time to turn the heat back on because you need several hours to bring it back up to the required number of degrees above your air temp setpoint in order for it to "shed" the required number of Btu's to accomodate the delta T inside to outside and maintain your space's indoor air temp (where the T'stat is located.)

That is not to say you can't reasonably use hydronics in an intermittently occupied space. I have some hydronically heated radiant ceilings (and radiant walls too but walls can pose a problem in a house due to picture hanging and such.). The thermal mass of sheetrock is relatively low so the lag is way less than in-slab. Radiant ceilings would work well in the office or any space with ceiling heights not very out of proportion to floor area. In spaces where the floor space is large then taller ceilings can be accommodated with radiant ceilings. Short ceilings, like 7 ft or less, will not be very satisfactory due to the hot head-cold feet issue. 8-10 ft ceilings work well. My ceilings in the areas with hydronically heated ceilings are 9 ft high.

It is all about radiant environment. Every thing in the universe radiates heat energy toward every other thing in the universe. When you walk up to a picture window in the winter and suddenly feel cooler, like there was a cold draft or something that is because your body is radiating IR out the window but the cold outdoors is not radiating much energy back to you so there is a sudden net loss. This deficit is perceived as that part of the room being colder even though a thermometer may say it is the same temp. Away from the window our body is receiving IR from the walls, floor, and ceiling as you radiate to the walls, floor, and ceiling. The net gain or loss is perceived as being in a warm or cool place.

Another thing about radiant heating. You will still probably end up with duct work for forced air for cooling since radiant cooling is even less well understood by HVAC practitioners than heating. You can't just pump cool water through the floor to lower the average radiant temperature in the space so you radiate out heat to the floor and feel cool like leaning against a concrete wall and feeling cool. It is altogether likely that the temps you would have to chill the floor to would be below the dew point and the floor would constantly "sweat" like the side of an Ice tea glass, not altogether wonderful for a carpet of even good footing on a slab floor.

Radiant cooling does work and is a wonderful thing when properly engineered and realized. Properly accomplished it dehumidifies and cools but is still often supplemented with an air handler and chilling coils. <font color="red"> Colorado is a semi-arid state and we are blessed with low humidity, so condensation is not as much of a problem for us. I do plan on a couple of ceiling fans in the shop area to help with summer cooling. I may also hang duct for an evil swamp cooler; but I would like to try one of these cooling units made by Coolerado of Colorado. http://www.coolerado.com/index.html They look and sound like snake oil; but I used to work at NREL (renewable energy lab) and I contacted my mechanical engineer friend who stills works there about these Coolerado units. His first reaction to them was the same as mine...snake oil; but he told me they are testing them at the lab and they do work. The downside is price. </font color>

An accurate as-built set of drawings/photographs of the in-floor slab pex installation is not an issue. The thermal time constant is the issue. It takes a long time to bring the slab up to temp and a long time for it to cool. It is NOT EFFICIENT because you will waste much more of the heat than you use. <font color="red"> Agreed, the as-built documentation is no big deal; but it's just one more item I would rather not have on the "to do list." </font color>

Another respondent mentioned solar. I'll not comment on the economics of a solar installation as there are just too many variables to allow adequate coverage of the topic in this post BUT once you are using solar energy to heat the floor it may be less important to you that such a large percentage of the heat is wasted in your absence. I considered a solar collector with thermo-siphon water "pumping" (cheap to build and cheap to operate) but decided against it and rely on my geothermal water to water heat pump (and two other high SEER air to air units) to handle my house (5000 + with 3 attached shops adding another 2300 sqft.) I am considering sharing a waste oil and or wood fired heater between my wood working shop (about 800 sqft) and the newly converted space (tractor shed to metal working/welding shop ( a tad over 1000 sq ft) just because I may want to. The new metal working shop (21x48ft) shares 24 ft of common wall with the wood working shop and extending the ducting for heat and air from the wood to metal shop is trivial (and some non trivial electric dampers and control electronics to zone it.)

Overhead gas fired radiant heat has a very rapid response time and recovers quickly from an "airing out." It is used to good effect in hangars and garages where large doors are frequently opened. The warmed air may escape but much of the comfort is provided by IR radiation and that works with the doors open and the space quickly recovers after the door(s) return to the closed position. Overhead radiant requires little or no advance notice because the radiant heat virtually instantly makes the space feel comfortable.

I was at the cattle auction today (selling 5 weaned steers at about 500 lbs each) and there were two large hydraulically operated doors, one to let stock into the sale ring and another to let them exit. The doors were opening over and over as each animal/group came through, yet, I had to take of my hat and coat and unzip the legs of my insulated bibs to not overheat due to overhead radiant heaters. They heat the objects in the room (people included) not just the air. Like a warm sun on a cold windy day.

Pat

[Pat]

Coolerado snake oil...

I have had some trouble explaining heat pipes to folks who don't have the appropriate background. Although to the uninitiated, heatpipes seem like snake oil or some sort of magic, they are real and are well proven in appropriate applications ranging from getting heat out of the interior electronics of the F-111 swing wing to cooling high performance CPU's in PC's. There are commercial packaged units for use in HVAC applications that are terrific enhancements to cooling systems (dehumidification), especially in humid climates or other situations with high latent loading.

I followed the link and read the material on the Coolerado system. The theory sounds OK but what remains to be seen is the mechanization/realization. There are lots of good ideas out there which have to wait until advances in the state of the art of manufacturing advances sufficiently to make them economically feasible. Maybe Coolerado is there.

If you don't want to be extravagantly wasteful with energy in heating an intermittently occupied space you need to carefully consider thermal mass and its effects on the time constant of your heat system (in this instance SYSTEM includes the building as well as the mechanical equipment.)

In a residence that has a high percentage of occupancy, thermal mass can be your friend, the big flywheel that helps level out variations. This is true for in-slab heating or similar. The reverse is true if you have an intermittently occupied space with a low percentage of time when it is occupied. In-slab heat in a workshop is a very comfortable thing but essentially has to be heated all through the heating season as the response time is so long you can't wait till you are there to turn the heat.

In the case of an intermittently occupied space with low percentage of occupancy, reducing the effective thermal mass is a good idea. Decoupling thermal mass from the occupied space allows faster response in heating and wastes less heat at shutdown. For example, in a tilt up concrete or cast in place wall system you would insulate the interior surface of the concrete wall to decouple the concrete's thermal mass from your "system."

Similarly, a fast response heating system would be good. Radiant heat is a good choice. Radiant heat raises the average radiant temperature of the space and can make it comfortable to occupy much faster than forced air (and its inevitable cold drafts at start up) and HOURS to days faster than in-slab. Radiant heat will make a space comfortable from a cold start faster than other systems. Because of this you don't need to spend energy far in advance to preheat the space and if your schedule is unpredictable you would either have to use the space cold or heat it all the time just in case. Not much of an issue with a good fast response radiant system.

I have an eclectic mix of system heating elements in my house which includes both in-slab, in-wall, and in-ceiling hydronics (and other non hydronic systems.) In-slab is NOT a candidate for setback strategies but in-ceiling can be for a space like a bedroom where the desired overnight temp you prefer may be several degrees different from the preferred daytime temp. Heated ceilings are quite compatible with plush carpeting (not so with in-slab as it raises required water temps above the practical limit for a heatpump and requires a boiler system.)

Rugs or carpets in your office space will raise the comfort level (in an intermittently heated sceanario) as it will decouple the slab floor from the radiant environment and increase perceived warmth (greatly diminishes the cold feet effect of cool slabs in a heated space.)

Way back when... I was the energy conservation officer at SUBASE San Diego and NREL was one of the fonts of knowledge I tapped for info.

Pat

[mjncad]

Pat:

You explained the pros &amp; cons of in-slab radiant heat for an outbuilding far better than I could. Thanks for doing that.

Since ceiling mounted radiant heaters heat objects just as in-slab radiant heat does; what are your thoughts on the following scenario?

A well insulated outbuilding with a concrete floor insulated from the earth by at least 2" of extruded polystyrene foam. Shop area heat is by ceiling mounted gas fired direct vent radiant heaters. Would the concrete still act as a thermal mass for storing and releasing heat; but not act as the source of heat as in-slab systems would be? I'm thinking this would give the best of both worlds for fast response to changes in temperature setpoint while getting some thermal mass value.

Thanks,

[Pat]

Will the floor still do the thermal mass mambo? I thought so before I observed how my house actually works. Of course you won't violate the laws of physics and the floor will tend/try (TRY, we always seem to anthropomorphize physical objects and processes as if they had a will of their own) to take on the average temperature of the room plus a little maybe because of the radiation of the ceiling. The floor, when decoupled from the dirt by 2 inches of rigid foam (what I used under my basement floor and outside the basement walls) will act as a bit of a thermal flywheel tending to take a weighted average of the radiant environment and air temp.

Lets say you ran the radiant heat in the space for 8 hours a day for several days. The floor will still not warm up as much as the air is warmed duiring the heated periods and will feel cold (at least cool) to the touch. My basement has been at or above 70F for several months with the southern fenestration and some heating from the mechanical spaces (lots of hot water piping) it hits 74 at times. This is with its zone stat turned off so it receives no forced air heating. Yet, the bare concrete portion of the walls (top half has carpet glued on it and bottom half will get eastern red cedar wainscot) will suck the heat out of you if you lean on it while waiting your turn to shoot on the pool table.

Your shop floors would not be comfortable to bare feet. My heated floors (not in shop) are toasty. If in your shop you put a carpet or rug on the slab floor the top surface of the rug or carpet will be heated much faster and to a higher degree by the radiant heat shining on it and make the space more comfortable when being heated. The net radiant environment will be elevated considerably and comfort will be increased with the carpet or rug. The R-value of the floor covering will reduce heat storage in the slab but its effect is not such a big deal anyway as a passive storage device.

The radiant heat will tend to warm the slab but the heat capacity of the slab is so large the change in temp in say 8 hours will not be much. Then in the intervening 16 hours before you power up the radiant again the slab will cool, giving up heat to warm the room a bot over what it would be with no slab floor. Eventually the weighted average temp of the slab will achieve its final value and not vary a lot from heat on to heat off, contributing just a little heat to the room overnight

I would still recommend insulating the slab. It will get warmer and it will buffer the temp during the heat-off periods some. I'd still not put any plumbing adjacent to the outside wall since the slab will not be heated and the plumbing will not likely be exposed to the radiant ceiling. If for example you wanted the office to heat up really quick you could use rigid foam insulation (fire retardant version please) over (probably not in place of) the sheetrock. A half inch or even a quarter inch would do the trick and you could paint it. It may not be sufficiently aesthetic but if you used foil lined rigid insulation installed foil side out and DID NOT PAINT it the radiant environment would take a sudden performance boost and the walls wold literally mirror the radiant heat of the ceiling. This is not practical in some instances.

Pat