This has been very interesting weather as we have been at or below design temp for some days now.  Nights have been 7F to 12F and days get about 17F to 25F, and I think design temp was 17F-19F, something like that.  In order for it to be this cold here, close to Puget Sound, we almost certainly have to have clear weather, so we have sunshine during the day.  (A thing worth remarking on during the Winter.)

The sunroom hits 75F less than 30 minutes after the sun gets it in the morning and we have been using it to kiln-dry 30 chunks of glu-lam destined to be stair treads.  It gets to 85F by about noon.

I was down in the mechanical room in the morning when I noticed that the air to water heat pump was silent and the circ pumps were hardly running.  Just before I went home the night before, they were running flat out, so I was worried until I saw that only one zone was calling for heat.  Sure enough, everything else was being heated by the passive solar.

With lows way below winter normals, the heat pump runs hard at night, but normally, if we had occupancy, we'd be running a wood stove in the evening and at night, and that would probably shut down the low COP nighttime runs.

So the bad news is that the sun does not shine that much in western Washington. The good news is that when it gets really cold, the sun does shine, and well-designed passive solar is finally able to demonstrate its beauty.

We have been having colder than normal weather here in Colorado, but it is almost always sunny in this area, with the additional benefit of snow on the ground lately that really allows the solar energy in. Unfortunately, I have limited windows on the south side and some shading, so there will still be a significant amount of natural gas used for heating in this cold snap. And we are yet to get to the historically coldest part of the year.

The good news is that when it gets really cold, the sun does shine, and well-designed passive solar is finally able to demonstrate its beauty.

Passive solar really does work well. Once the clouds roll in , the warmth goes back up and the heat pumps are back in high COP territory. I just noticed my neighbor has gone through more than 300 gal of propane in less than two weeks, and he isn't even home. His place is 2/3 the size of this one.

Posted By ICFHybrid on 08 Dec 2013 07:54 PM

The sunroom hits 75F less than 30 minutes after the sun gets it in the morning and we have been using it to kiln-dry 30 chunks of glu-lam destined to be stair treads.  It gets to 85F by about noon.

What is the SHGC of the windows? How much glazing is there? Any pics?

The sunroom is 100% glazed, including 2:12 pitch roof. It shares one wall with the house, but sticks out on three sides. There is an 18" framed kneewall with masonry finish around the outside perimeter. All glazing units are double pane glass with Argon fill. The over head (roof) units are coated to restrict solar radiation at low angles of incidence (e.g. direct sunlight at 90 degrees). There is also some light tinting and I can't remember if this is a consequence of the glass coating or the glass itself. You can think of the overhead as being Low SHGC. On the other hand, the sidewall units are coated to reflect at high angles of incidence and appear more clear than the overhead. You can think of these as being High SHGC.

What this gets you, particularly for our WA location at 48N is that Summer insolation is restricted on the roof and sidewalls, while Winter insolation is generally absorbed, for both sidewalls and roof.

For anyone wishing to do similar, I will remind that you have to provide for Summer cooling. If this place can get 85F or 90F in Winter, you can imagine what happens in the Summer. I put a motorized skylight opener in the highest part of the roof. When the temp reaches a setpoint, the skylight opens. It also opens a small motorized window unit at the level of the kneewall, creating a powerful stack effect. The flow-through ventilation continues until the temperature drops, at which point the skylight and window close, retaining heat for the evening and night.

Are you saying that your passive solar heating is resulting in some zones overheating to 85-95F during Winter clear sky irradiance with outdoor temps below design temp? If so, this would indicate the passive solar design is way off the mark. What is your hydronic floor heating system doing during the passive solar irradiance period? Hopefully the passive solar heating and hydronic floor heating systems were integrated and the hydronic floor heating system just doesn't shutdown during the passive solar irradiance period and let any floor zone temps get below the required temps. The hydronic floor heating system should be moving the excess heat from the floor zones that are experiencing the irradiance to the floor zones that are not experiencing the irradiance, yet still need to provide heat so as to maintain the desired temps in all the zones while reducing your active heating fuel usage and associated costs.

If we circulate into the house, the temperature in the sunroom does not stay at 85F. We are restricting circulation in order to dry the glulams more quickly. In any case, it wouldn't indicate that the design is "way off", just that the system was optimized for something else, which in Western Washington is gray, overcast weather.

The hydronic floor heating system will continue to circulate via override, and that is because it operates at such a low temperature, it will actually return heat to the entire system. It's a giant solar collector.

Nicely done ICF and yes, even if it operated at a higher supply temp, the zone receiving the irradiance heat would still return a higher temp than the supply temp...that's the beauty of using your irradiated floor zone in lieu of your normal hydronic heating source to heat your entire building during the irradiance period...and hence our logo, eh! Directly exposed thermal mass will absorb 60-85% of irradiance heat no matter what temp the thermal mass is at depending on the surface color and material composition. So as long as your design keeps the sum of the unabsorbed irradiance heat gain and the thermal mass convection/radiation heat gain (which is solely a function of the thermal mass temp and controlled by the hydronic system) in close alignment with your actual building heat loss, you are golden.

Normally for a "pure" passive solar heating system, you would design for less clear sky heat gain than your forecast heat loss at your average monthly outdoor temps to avoid risk of overheating while still significantly reducing your active heating fuel usage and associated costs. Folks often end up creating an overheating situation at various times of the year when they ignore or push this limit.

However, when you integrate both heating systems, you can design for much more irradiance heat gain without any risk of overheating. Nevertheless, you still have to carefully consider your window area and mitigate/address the associated heat loss that will occur during non clear sky daytime periods and during night time periods.

I have been reading elsewhere that passive solar is dead. Is there a revival going on? Personally, I like the idea of passive solar. To me it seems a "no brainer" i.e. to get something for nothing that doesn't involve burning fossil fuel.

Is there any particular heating system that goes well with passive solar?

The hydronic floor heating system will continue to circulate via override,

ICFHybrid - What are you controlling your system with? Do you get to pick which zones you want the heat to go to?

Hydronic radiant floor heating and masonry heaters are compatible with passive solar...since all are radiant emitters and all use thermal mass. Properly integrating a hydronic radiant floor heating system with passive solar allows you to get much more aggressive with passive solar heating while eliminating any risk of building overheating.

Passive solar is very much alive and well. However, there are many so called passive solar experts who are completely ignorant with regard to how to properly design a passive solar building. They also typically charge a ransom for their poor passive solar house plans or design expertise. The vast majority of passive solar buildings were very poorly designed and this has not helped the reputation of passive solar. The same can be said for hydronic radiant floor heating too. Any time something gets popular, you can always count on a large number of clowns getting into the business and creating problems for clueless consumers. If you encounter an architect selling passive solar house plans or a passive solar design expert using anything like the following two "rules of thumb", hold your purse/wallet very tightly and run for the hills:

1) A passive solar building should have a total south wall passive fenestration area between 7-12% of the total building area.

2) For every square foot of south wall passive solar fenestration area in excess of the 7%, a passive solar building should have 5.5 square feet of 4 inch thick thermal mass material.

A good passive solar building design is similar to a good building heat loss analysis. So you should consider finding an experienced engineer who fully understands solar heat gain, heat transfer analysis, and is capable of carefully aligning all these heat BTUs to achieve a successful design.

You may find the passive solar design software and associated instructional information on our website to be both educational and enlightening. People have complimented our passive solar information for being more useful than most of the lame books published about passive solar.

Do you get to pick which zones you want the heat to go to?

Not manually. It's pretty simple Uponor Zoned Logic. If a zone is calling for heat via thermostat, the valve opens and the zone gets circulated.

So when you put it in override, you are doing that manually? and you have to manually override the another zone to send the heat to?

I was hoping maybe one the controllers had a script to sense overheat and then send it where its need most. Maybe in time.

We use PLRs (Programmable Logic Relays) and our own proprietary software algorithm to control our integrated hydronic radiant floor heating and passive solar heating systems. I am not aware of any existing commercial-of-the-shelf product that would readily enable properly accomplishing this. Our software control algorithm uses the actual building latitude and longitude and building orientation, roof overhang and fenestration geometries plus sensor feedback of irradiance magnitude, actual outdoor temp, forecast outdoor temp, indoor zone air temps, zone thermal mass (e.g., slab floors and masonry walls) temps, zone hydronic supply temps, zone hydronic return temps and date/time. It is also important to properly zone the thermal mass irradiance areas of the building so you have the required control authority.

You don't EVER want to sense an overheat situation because by then it is too late.  Thermal mass temps can't be changed quickly enough to handle variable irradiance heat gain and variable building heat loss conditions just using a standard commercial reactive control system.  You need an intelligent control algorithm that can generate what control system engineers call "phase lead" and a heating system that provides sufficient control authority (i.e., heat transfer capability to handle worse case changing conditions) so as to NEVER allow an overheat situation (or an under heat situation) to develop in the first place.

The room has two thermostats. When it is too cold, the primary calls for heat from the modulated heat pump. When it is too warm, the secondary overrides the valve, keeping the loop open so the heat can be shared.

We have the place wired for sense and control up the wazoo, but so far, everything has worked remarkably well on simple thermostat controlled zoning. No need for all that fancy software control.

So what happens when the second stat holds the valve open and the rest of the house doesn't need any heat - no heat demand? What triggers the circ pump? Just the end switch on the zone valve?

Would be nice if it also trigger say a basement zone so you could store the extra heat in the slab where it could radiate up into the house over nite.

sailaway

•••I am not aware of any existing commercial-of-the-shelf product that would readily enable properly accomplishing this.•••

So get of your butt and market one. (actually most of that would be done sitting down ;-)

Nothing fancy with lats and longs

Just has to say -- this floor is too hot, where should we send this extra heat. It should then pick the lowest zone that has room for more btus and default to the basement slab or a water tank or something if it would not be practical to add more to a floor zone.

For you guys that like naked mass, this would make it easy to move heat from a living area with direct exposure to back room with none.

For me, I would just store the heat in the slabs or water tank and return it to the house at night.

OK, if none of the zones are calling for heat, but the sunroom is too hot,the the valve is held open and the pump circulates, but the warm fluid has no where to go because all the other zones are closed off. There is no point sending it to any of the other zones "to store the extra" because they are not calling for heat. That would only make them too warm.

Once the coolest zone calls for heat again, the Altherma looks at the returning fluid, sees that it is above return temp and doesn't turn on until it looks more like a proper return temp. The Alpha pumps run in adaptive mode, so they slow way down when they are just circulating the single zone and ramp up as the various zones are opened up.

We market our design/build expertise having been the first to accomplish this.  There's really no need to market the hardware. We prefer the Allen Bradley Micro800 family of PLRs that are even cheaper than most commercial controllers for hydronic systems. The reason we use a PLR and a sophisticated control algorithm is to ensure precise temp control of +- 1F for all the zones given the variable irradiance heat gain (which is often huge given our aggressive designs) and given the variable building heat loss conditions. Latitude and longitude are required so the controller can accurately forecast what the irradiance magnitude will be for every hour of the irradance period given the building orientation, roof overhang, and fenestration geometries.  Again, high thermal mass integrated passive solar and hydronic radiant floor heating systems need plenty of phase lead in order to provide this level of controllability.

As you indicated, heat is moved from the thermal mass (e.g., slab floors and masonry walls) zones receiving irradiance to the other thermal mass zones that continue to provide heat as normal. In simple terms, the thermal mass zones absorbing the irradiance operate at a lower thermal mass temp than normal to compensate for the unabsorbed irradiance that heats the zone so as to keep these zones at their normal desired temps. In other words, we don't allow the passive solar irradiance to ever overheat these zones and we don't need to open windows or provide mechanical ventilation to accomplish this either. The other thermal mass zones just continue to operate at their normal thermal mass temps so as to keep those zones at their normal desired temps, but using the free surplus heat from the irradiated thermal mass zones. Slabs are not a good place to store heat as slabs lose heat quickly and you don't want to overheat the zones these slabs would be located. A well insulated building typically operates with the thermal mass emitters at only about 74F. Insulated water tanks are a good place to store heat, but add significant complexity and cost to the system. If you are happy with a 50-70% heating energy/cost savings, you don't need really additional heat storage beyond what you load into all the high thermal mass zones during the irradiance period.

Latitude and longitude are required so the controller can accurately forecast what the irradiance magnitude will be

How does the controller know what the weather will be?