Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
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Fundamentals of indoor environmental quality / thermal comfort and air quality solutions using radiant based HVAC

A note on humidity:

Many people try to cool themselves with lower room temperatures when in fact the problem could be humidity. By lowering the humidity in the space and increasing air velocity with ceiling fans (or similar) many occupants can sense and perceive cooling without running traditional A/C systems.

For additional cooling techniques see:

Humidity: An Important Nexus in Indoor Environmental Engineering

Thermal comfort analysis with elevated air speed and moderate humidity, SI and IP screen shots.

For help in understanding this tool see any one of our 2016 thermal comfort slide presentations; or sign up for our 2017 programs as they become available.

 

Why do homes need Tinkerbell and pixie dust?


Because the design and build process happened in Never Neverland.

Image source:
https://en.wikipedia.org

Overheating Doesn’t Happen in Never Neverland: Peter Pan is in The House
Copyright 2016, Robert Bean, R.E.T., P.L. (Eng.) All world rights reserved. Originally in HPAC Magazine Canada Fall 2016

Recently Wilma Leung, my new favorite sage and her progressive team from BC Housing / HPO hosted 340 builders and affiliated service providers from British Columbia to participate in my class on thermal comfort for vulnerable populations. The program included passive cooling and solar control techniques for mitigating overheating risks during climate changes of consequence.

Now you don’t have to be a climatologist or frontline healthcare worker to understand aggressive thermal changes affect vulnerable populations as heat related morbidity and mortality reports increase across the planet. Concern is specifically for infants, infirm, injured, and elderly and others in palliative care environments. This group spends more time indoors, are unable to find refuge from the heat, and are unable to or find it difficult to adapt.

It would be nave for residential HVAC designers to observe this specific combination of demographics and climate change from the perspective of a spectator. Why? Because your clients or their relations have a high probability of entering one or more dimensions in the vulnerable category. Statistically most will want to navigate that experience in familiar surroundings of home rather than the confines of an institution. But consider the significance in choosing the indoor environmental quality and vigor of a modern healthcare facility versus that of a code built house. The former designed to promote healing and built to function during environmental stress and/or failures in infrastructure. The latter by default a satellite extension of the former but only designed to reduce the probability of illness.

Arguably code built homes are designed for aesthetics rather than resiliency. Thing is…the last time I checked there wasn’t any doctrine to say we can’t covet for our homes the quality environmental systems found in modern healthcare.

Peter Pan in HVAC Land

Setting aside the exceptions, residential HVAC designers employed in the distribution chain generally practice in a Peter Pan world where clients never become old, injured or sick. For the most part the residents potential palliative needs or needs due to changes in the earth’s environment isn’t even on the radar screen for discussion as builders frequently isolate the purchaser from the design technician. The majority of practitioners simply by choice or direction take a passive position within a segregated construction system; only a few become active participants on integrated design teams.

In the first scenario the design business follows the status quo, resigned to have zero influence on property schemes, architectural, interior and building systems. There is no motivation or there is prevention to reach out to the client to actually ask what they want in mitigating problems in the event the home and/or occupants become at risk due changes in health and/or the environment.

In this scenario the designer accepts the construction drawings as delivered to the office, load calculations are performed as per minimum requirements, and schematics developed based on first cost rather than life cycle cost. Then specifications and equipment lists are prepared and sent out for tendering where typically the lowest cost prevails. It’s unfortunate but this represents the majority of residential design practices across North America and ultimately creates for some occupants a need for Tinkerbell and her pixie dust.

At the other end of the spectrum is the forward thinking educated client who lives outside of Never Neverland and is fully engaged in reality. They are looking for that integrated HVAC designer to influence the architecture, building orientation and enclosure; and materials and methods of construction. It is here in the latter approach where significant differences can be made for and on behalf of the family.

Since we’re talking about rising temperatures and staying cool, let’s look at some strategies and tactics that can be used to control overheating at times when people need comforting care environments during failures of one form or another.

Strategies and Tactics

First let’s state the obvious - the number one reason for overheating is a radiant problem. That being the shortwave high intensity solar energy absorbed by and transmitted through into the building. Poor to no shading, inadequate enclosures and high window to wall ratios are the major culprits here. Second to this is internal loads created by the conversion of shortwave to longwave energy vis a vis absorption and conduction; plus radiant (and convective) loads from people, lights, appliances and IT/entertainment equipment.

All of the above raises the mean radiant temperature (MRT) which retards the shedding of body heat. Why we try to solve predominantly MRT problems with convective solutions is a testament to habits gone bad.

To solve the radiant problem you’re going to need to understand how earth revolves around that big lamp in the sky and how that path affects the real estate being developed. There are many free online solar path tools but my favorites are those developed by Dr. Andrew Marsh. Shown in Figure 1 is how that solar load on a random spot in western Canada on June 21 looks like from outer space.

Figure 1 is how that solar load on a random spot in western Canada on June 21st looks like from outer space.

Figure 2 is the sun path for Figure 1 at the same location.


Figure 2 (above) is the sun path details for the same location and Figure 3 (below) illustrates the exposure and shading at the same location (mid morning) for a hypothetical city populated by various building geometries.

Figure 3 Mid-morning solar exposure on the east and south facades and shading result for a hypothetical city in western Canada.


Figure 3 Mid-morning solar exposure on the east and south facades and shading result for a hypothetical city in western Canada. Now consider the sun paths and the solar irradiance at the Earth's atmosphere of about 1.36 kW/m2 of which approximately 1000 W/m2 makes it to the earth surface when measured perpendicular to the sun. Even when measured through various filters (i.e. clouds, particulate) at various altitudes throughout the year it is still a lot of energy that gets absorbed and transmitted into the building (see figure 4).

Figure 4 This is a 750 Watt heat lamp. Imagine one of these on every m2 of solar exposed surface.


Figure 4 is a 750 Watt heat lamp. Imagine one of these on every m2 of solar exposed surface. That is a lot of energy that gets absorbed and transmitted into the building which if not controlled leads to an increase in the MRT leading to overheating of the occupants. So the first non-mechanical strategy to prevent overheating when, “designing for failure” is to stop the shortwave radiation from hitting the building. Unfortunately 100% success would be equivalent to living inside a shaded bubble which is neither desirable nor practical.

So here’s some practical tactics that you the HVAC designer should be discussing with your clients to eliminate or reduce mechanical cooling or at the very least to enable peak performance from cooling equipment when absolutely needed.
 

1. Building orientation and shading

Fixed overhead shading (includes roof overhangs) doesn’t work on eastern and western exposures but can work on the south during cooling season; use windows inset into the structure with adjustable exterior horizontal or vertical shading on the east and west exposures (see Figure 5). When possible orientate the building on an east-west axis.

Figure 5 fixed overhead shading (includes roof overhangs) doesn’t work on eastern and western exposures but can work on the south during cooling season. Note how with this aspect ratio how a north-south orientation exposes more surface area to solar loads known for their shading difficulties.
 

2. Use exterior window shading as discussed below and as shown in Figure 6 (types a through j).

 

Type a: A wall is the perfect window for HVAC engineers. It has a 100% shading effectiveness and if built properly it is secure, doesn’t leak, has a low thermal load and is effective at reducing air and sound pollution. It’s only flaws are, you can’t see out of it and it lets no light in. What? Is this a problem? Type b: This is the project budget window; large, clear, no shades, cheap and lots of them.

 

Type c: This is the bare minimum window, double pane, single coating, no exterior or interior shades. Solar coatings are good but both b. and c. still allow short wave energy to hit 100% of the glass surface area thus the 0% shading effectiveness. Type d: Getting clients to use exterior fins or inset windows puts you into a new league – congrats! They work on southern exposures and can work on some north east and north west exposures. Up to 70% shading effectiveness.

 

Type e: Brise solei will put you in with the architectural crowd but only if you pronounce it correctly. Works on southern exposures but not the east or west. Works with windows which swing both ways (hoppers, awnings, casement).(4) Up to 70% shading effectiveness. Type f: Horizontal louvers work on all exposures when adjustable. They don’t work with windows which swing outward - only inward, sliders and double hung. More stable in windy climates, but can accumulate snow, bird droppings etc. Up to 90% shading effectiveness.

 

Type g: Vertical louvers as above except no snow, bird droppings etc. Type h: Roller shades, as above but better efficacy depending on openness factor. Up to 95% shading effectiveness.

 

Type i: Venetian blinds as per type f and type g but better rangeability. Some types not suited for windy climates. They also don’t work with windows which swing outward only inward, double hung and sliders. Up to 95% shading effectiveness. Type j: Shutters - still and always the classic solution. They don’t work with windows which swing outward only inward, double hung and sliders. Up to 100% shading effectiveness.
 

Figure 6 Exterior window shading options (above) can significantly reduce solar loads and when used with other tactics can in some case eliminate the need for mechanical cooling.


3. Window Orientation and Wind Patterns

Figure 7 For climates where night time ventilation cooling is possible, try to integrate window orientation and types with prevailing summer wind patterns
 

4. Use window types which enable natural ventilation and can be fitted with exterior shades; i.e. swing inward, sliders, double hung etc. (see figure 7).
 

5. Complex building geometry equals increases in surface area, thermal bridging, infiltration and moisture penetration all which lead to increases in interior temperatures and moisture. Simple building shapes using advanced framing techniques are better.

Figure 7a Complex geometry (L) increases the risk of the outside getting inside, is more expensive to frame and finish and the primary location for first and repetitive failures. Simple shapes (R) make much better buildings from a performance perspective. Some architects get simple, others do not. Those that like complex don't have to live with the results of complexity. The same is true with mechanical and electrical systems. Words of advice: every original work of complex art remains long after the artist has died at which point the artist no longer cares what you bought.
 

6. Use high performance light coloured enclosures reducing U values, bridging and solar gains through exterior shading and windows orientated for natural ventilation (see figure 8). The enclosure specification for cold climates work for the summer; use R60 roofs, R40 above grade walls and cantilevered floors, R20 below grade walls, R10 slabs and min. R4 windows with <.25 SHGC. The width of overhangs should be a minimum of 50% of the height of the window or glass doors. Window to wall ratios should be kept below 40% (see figure 9).
 

Figure 8 Use high performance light coloured enclosures reducing U values, bridging and solar gains through exterior shades and windows orientated for natural ventilation.

Figure 9 Window to wall ratios of less than 40% are good, 30% is better. Even I draw the line at 20% everybody needs some natural light. Over 40% promotes excessive daylighting, destroys thermal comfort, enables fabric fading and VOC emissions and significantly increases HVAC loads
 

7. Use architecture to create solar refuge zones; north side, below grade, heavy mass enclosure. Think north side courtyards either enclosed or open. If they can take advantage of cool night time ventilation air all the better, if not use fans (see figure 10).

Figure 10. Use architecture to create solar refuge zones; north side, below grade, heavy mass enclosure. Think northside courtyards either enclosed or open. If they can take advantage of cool night time ventilation all the better. If not use fans.

 

8. Use property shading starting with soft and hardscapes such as trees and Pergolas.
 

9. If you do the above and still need active mechanical cooling then size your system based on night time loads. Run the system to cool the building mass during the evening, seal the house up during the day and ventilate only as necessary (see Figure 11). This strategy works exceptionally well with high mass enclosures with embedded cooling pipes.

Figure 11 Cool the building in the dark hours when sensible loads are lowest.
 

10. If outdoor humidity is a problem forget the natural ventilation. Seal up the home and use a dedicated dehumidification system. By lowering the absolute moisture in the space, increasing air velocity with fans and encouraging or enabling reductions in clothing you can solve the majority of overheating problems – but only if you get the building and mechanical ventilation system right!

 

Short Stokes

These shading and ventilation strategies and tactics work on all building types using air based systems, hydronic systems or hybrid systems. Take advantage of your local climate. Below grade soil temperatures are always cooler than above grade air temperatures. Use trees. Put window shades on the outside. Work window locations and selections into wind patterns. Night time naturally ventilated cooling works in many parts of the country. Low humidity, high air velocity and near naked works…just stay hydrated. If necessary, consider using non compressor cooling methods as discussed in the May 2016 Radiative Cooling article. If you still can’t convince your clients and their architects to employ these sustainable principles, we have been teaching our students to use the CBE Thermal Comfort Tool and its new solar calculator to shame them into submission (see figure 12). When it comes to architectural choices leading to overheating, guilt and reality are two gifts that keep on giving.

Figure 12 CBE Thermal Comfort Tool - shortwave radiation calculator. The best tool to get clients and architects to evaluate fenestration performance and WWR’s

 

References:

1. Hales, S., Edwards, S.J., Kovats, R.S.. Impacts on health of climate extremes, World Health Organization < http://www.who.int/globalchange/publications/climatechangechap5.pdf > accessed August 2016
2. A Human Health Perspective On Climate Change A Report Outlining the Research Needs on the Human Health Effects of Climate Change. Environmental Health Perspectives and the National Institute of Environmental Health Sciences. April 22, 2010 accessed August 2016
3. Marsh, A. Sun Path Tools < http://andrewmarsh.com/software/> accessed August 2016

4.
Engineers don’t judge we’re only concerned about performance.
5. Canadians deliberately put the letter “u” in the word mould and louvers. When Americans spell these words without the “u” it changes the entire meaning.

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