Saturday, April 28, 2012

Electrical Overkill: Heat Tape and Overlighting

Perhaps the thing I like best about doing energy audits is when I run into something that was not just poorly designed....it is completely idiotic.  Had two such situations yesterday.

The first one was actually described to me by a co-worker, but certainly merits inclusion here.  This building formerly had a cavity for utilities between the garage ceiling and the concrete plank above.  The ceiling was in disrepair, so it was removed.  What my buddy found was a large amount of piping in this cavity, with heat tracer tape wrapping EVERYTHING!  There was heat tape on the domestic cold water lines (normal), there was heat tape on the heating hot water supply piping (not normal), and there was heat tape on the chilled water supply piping (what???).  Furthermore, ALL of the heat tape was turned on, and there were no thermostatic controls or anything.  Think about this in the summer time....the heat tape is wrapping the chilled water supply....HEATING THE CHILLED WATER!  This is wasting electric several times over...and it is hilarious to think about somebody consciously deciding to wrap this stuff around chilled water piping.

The pic only shows half of the lights on THIS LEVEL of the stairwell!


Yesterday, I also saw a pretty ridiculous waste of electric.  I stepped out of the garage and into a stairwell at a 1 year old LEED-certified building in NYC.  Picture this: the entry door opened to a landing in the stairwell, which was an extra-wide stairwell.  From that point, the stairs lead both up and down.  If you can picture this, from the landing, all I could see was a flight of stairs leading up, a flight of stairs leading down, and the landing itself that I was standing on.  There were EIGHT 48" long T8 flourescent light fixtures in this area....probably 3x's more than required for adequate light levels.  Its like the lighting designer got click-happy in the CAD drawings or something.  Pretty ridiculous.

Thursday, April 19, 2012

Ventilation Reduction in Multifamily

Spent yesterday, an overcast Wednesday in April, testing ventilation rates on the roof of a 25 story multifamily building in NJ.  HOW DID I GET A WICKED SUN BURN?  It was overcast, slight rain, and its APRIL!  I look like a hot-house tomato today.  Unbelievable.

The goal of our work was to get a thorough understanding of baseline exhaust ventilation loads.  We will be looking to dial-back and "right size" the ventilation loads, and also to balance the system for optimized indoor air quality.

We tested 26 fans on the roofs of two attached buildings in the same complex.  Eighteen of the fans were up-blast, mushroom-style fans, which exhausted the bathrooms within the apartments.  We tested these using an innovative technique my firm has developed with a blower door.  The remaining 8 fans were side-blast utility exhaust fans, which are ventilating kitchens within the building.  These were tested with a similarly innovative technique that involves fitting a calibrated flow hood over the fan and measuring laminar discharge velocities with a hot-wire anemometer traverse.  Good stuff all around.

The results of the field-testing shows that the building is about 40% over-ventilated while being significantly out of balance.  We will recommend cleaning the sheet metal ventilation riser shafts, sealing them with a spray applied duct mastic, installing constant airflow regulator (CAR) dampers at every exhaust inlet to balance flows up-and-down the building, and installing new direct-drive exhaust fans with ECM motors.  We anticipate the building will realize substantial energy reductions related to the reduction in total ventilation.  For the layperson, every CFM of exhaust we can reduce is a CFM of air that already been conditioned and thus contains concentrated embodied energy.  Most buildings are significantly over-ventilated; right-sizing ventilation loads saves energy and money.

Also involved with this project is the installation of an HRV, which will allow the energy contained within the remaining exhaust to be partially recovered and re-introduced to the building.  More good stuff.

This project will receive funding from a public utility program and will provide an excellent case-study in the effectiveness of ventilation retrofits on existing multifamily buildings.

Yeah!

UPDATE: 4/24/2012
Calculations have shown that the building is actually 56% over-ventilated, rather than the 40% initially assumed, making this measure considerably more cost-effective than suspected.  Kitchens are exhausting around 100 CFM, and bathrooms around 50-75 CFM.  We will right-size the load on all of them to 30 CFM, which will allow for ASHRAE 60.2 compliant residential air change rates.  Yeah!

Wednesday, March 28, 2012

Optimizing Boiler Controls for Energy Efficiency

Well, my attempt to increase the frequency of my posting in March fell by the wayside.  First one.  Almost 1 month since I last posted.  I'm hopeful that I will give a better effort as we move into Spring.  My bad.

Today, boiler controls.  More specifically, touching on two specific Honeywell products I come across: the L91B proportioning (modulating) pressuretrol, and the L8124A aquastat relay, and working to optimize their set points for improved energy efficiency.


L91B: Modulating Pressuretrol
This is a really neat product I typically see on steam boilers.  Bellows within the base of the control swell and recede based on the pressure within the system.  This function works to modulate the current flow based on load demand: when load is close to being satisfied and pressure in the boiler builds, the bellows swell, and a potentiometer reacts by reducing the flow of current.  This drives the burner toward low fire in an effort to meet the reduced load demand.  Conversely, when boiler pressure drops, the bellows recede and the potentiometer reacts by increasing the flow of current and driving the burner into a higher firing rate to meet the load.  

The beauty of this control is that it will modulate as needed to keep a steady firing rate at a desired system pressure.  This is good for both energy efficiency and wear and tear on the system.  The problem is that the dang things are almost never set properly.  

The differential on the L91B is additive; the operating range of modulation is equal to the Main set point plus the differential.  This must be configured carefully with regard to the Operating Pressuretrol set points.  Too often, the settings are incorrect.  The entire range of modulation for the L91B should occur within the range of the Operating Pressuretrol (which, to confuse the situation, has a subtractive differential).  Basically, you don't want the burner to cut-out on high limit while still the L91B is still modulating the firing rate.  The L91B Main+Diff should be slightly less than the cut-out setting for the Operating Pressuretrol.  Also, the Diff on the L91B directs the rate of modulation; a small Diff means a more aggressive rate of modulation, while a larger Diff means a more subtle rate of modulation.  This can be important to fuel consumption and other system operating functions.

Retro-commissioning the L91B so that it is appropriately configured will provide even and efficient combustion across the entire firing range.

L8124A: Aquastat Relay
I often see this Honeywell control on small home hydronic systems, specifically where there is a single boiler that provides for both space heating and domestic hot water needs.  This relay control has a high limit adjustable setting with a fixed Diff of 10F, and a low limit adjustable setting with an adjustable Diff range of 10F-25F. 

The low-limit is going to control the DHW, and the high limit is going to control the space heating.  I last saw this over the past weekend at a buddy's house.  They are getting killed by their oil consumption, exacerbated by $3.90/gallon fuel oil prices.  This is a tiny house with fine-tube convector baseboards and a Weil-McLain Gold series oil boiler.  The L8124 was set to 185F at the hi-limit for the baseboards (10F fixed Diff) and 160F with a Diff of 25 at the low-limit for the DHW.  With this setting, the burner will fire at low-limit between 135F-160F, and at high-limit between 175F-185F.  I feel that both of these settings are inappropriate.

This house is tiny and there is ample radiation.  I turned the hi-limit control down to 175F so that the burner fires to maintain a range of 165F-175F at a call for heat, which should be more than enough to heat this home.  I changed the setting of the low-limit to 150F with a Diff of 10F, so that the burner fires between 140F-150F, which should be more appropriate.  Reducing the low-limit target temp will bring down the excessively high DHW temp of 160F, which needs to be mixed down at the tap to prevent scalding.  Reducing the Diff will reduce total burner firing time, which should improve fuel efficiency.  This will promote more frequent cycling (short cycling), but that shouldn't be an issue with a low mass boiler housed within conditioned space.

Unfortunately, this scenario is really trying to do a little bit better with a sub-optimal configuration.  A larger differential on the low-limit will allow the burner to remain off for longer periods of time, but will then require the burner to have longer on-cycles to achieve the set point.  In this case, there is just no reason to be making DHW at 160F; that is too hot and potentially dangers.  The new setpoint of 150F is still too hot, but less too hot and less potentially dangerous.  I would love to be able to leave it at 150F and crank the Diff up to 25F so the burner fires only between 125F-150F.  Unfortunately, the boiler has minimum hot water return temperatures to ensure condensation does not occur in the flue, so we can't go below 140F.  For this reason, a standard, open combustion boiler with a tankless coil is not an ideal method of producing DHW; sometimes you just gotta work with what you got.

The moral of the story is to scrutinize boiler controls, consult manufacturer's specs, and make some changes to the protocol where appropriate.  You can often tweak a few percentage points of heating fuel savings by making adjustments to optimize settings.

Wednesday, February 29, 2012

Retro-commissioning boiler controls

Only my 2nd post in February, and today only qualifies as February because of the leap year.  I'll try to do better in the future.

Tekmar makes a few excellent panels for boiler control and operation.  The panel can perform tasks such as controlling scheduling and reset functions, staging boiler operation, prioritizing boilers for DHW production, controlling circulating pump operation, lead/lag, and more.  The Tekmar is an advanced control with well-engineered features, suitable for a wide range of applications.

I spent about 8 hours yesterday flipping through Tekmar settings during a retro-commissioning project.  Amazing to see how poorly many of these panels were configured by the installing contractor, with no effort given to optimizing system performance.  Get paid to install it, and then leave it alone, I guess.

We went through and corrected/optimized settings for each of the 5 buildings we were in.  We fine tuned desired indoor temperatures, reset schedules, warm weather shut down set points, DHW temperature controls, circulator operation, etc.  For example, at one of the buildings, the minimum hot water supply temperature was set to 180F.  Because of this setting, the coolest the boiler could send water to the building was 180F, meaning that night time, outdoor, and warm weather reset functions had all been bypassed.  We expect that the retro-commissioning on these panels will save about 3-5% of the buildings heating fuel consumption.

These panels are fine pieces of equipment capable of generating real energy savings through tightly controlled operating parameters.  But when they are not set up properly and commissioned at the time of installation, the chances are that they are performing well below their capabilities.  When you come across these, push the owner to invest in a retro-commissioning program, which will be cost effective and will allow the building better control over their systems.

Thursday, February 2, 2012

Arizona duct sealing for IAQ

Just took a random trip out to Arizona to visit the ‘rents.  Leaving North Jersey in late January and getting 4 straight days of 70 degrees and sunny in the desert.  Not bad.  I can certainly understand the appeal of this place…really is gorgeous, especially when it’s not oppressively hot.
Anywho, I always like to poke around in a different type of house when I get the chance.  Adobe style, 2500 sq ft, 2 heat pump HVAC systems, built in the 1970’s with an addition in the 1990’s, slab on grade, flat roof.   North Jersey is not exactly known for slab-on-grade, fully stuccoed, adobe style houses that exist in dominant cooling climates.  So with my pops leading the way, I got a little tour of the house and came across an interesting little building science related tid bit.
My folks had an energy audit done on the house about 6 months ago.  A gentleman from the utility company came out and performed what, by my father’s account, seems to have been a solid and thorough energy audit adhering to BPI standards.  Blower door, some pressure diagnostics, and analysis of the ducted distribution system and AC/heat pump systems….pretty good deal for $100.
The guy ran the blower door with and without all of the duct work taped off to determine the estimated air leakage attributed to exterior duct leakage.  The auditor also determined probable (not measured) HVAC system airflow, and determined that estimated duct leakage to the outside was approximately 25% of total system airflow.  Pretty typical.
With this knowledge in hand, I took a closer look at the HVAC systems.  System #1 is a 3-ton unit located in the garage and services the front (original) 2/3 of the home.  System #2 is a 2-ton rooftop packaged unit and services the master suite and rear 1/3 of the home.  The rooftop unit looked pretty tight, so I focused my attention on the garage unit, which looked something like this:
The field built plenum was banged together with a few standard framing nails, and a very weak attempt was made at sealing the inside of the plenum with Great Stuff.  A non-treated 2x4 sill plate was shot into the garage slab as a nailer for the plywood.  Obviously, the 2x4 is starting to rot away.  A filter slot and an opening for the since-removed evaporative cooler in the supply trunk were basically wide open to the garage.

Re-calling all they did for me growing up, I decided to tackle the job of sealing up this air handler and plenum.  We picked up a few cans of Great Stuff and a tub of water based duct mastic, and I went to work.  I popped off the front piece of plywood and literally crawled into the plenum.  Vacuumed out the nastiness in this area, and then spent about 30 mins and an entire can of great stuff sealing up all accessible penetrations between the garage and the plywood box.  I then pulled off all of the failing metal tape at the seams in the duct work and painted it up nice with the duct mastic.  I sealed off the penetration for the evaporative cooler, and my pops will be weatherstripping the door to the filter slot.  I sealed up the “access door” to the plenum with duct mastic.

This was all a pretty typical case of duct leakage outside of the envelope.  Seal up the ductwork and improvements will be had.  Three specific results are expected:

-          1.  IAQ improvements.   My parents have an IAQ issue where the house sometimes smells like garbage.  The plenum is technically on the return side of the system and as such is under a continuous negative operating pressure.  This negative pressure draws air partially from the garage and distributes it throughout the home.  Garage air is not good….chemicals are often stored there, and CO is exhausted from cars when they are started.  More importantly to my parents, though, is the IAQ issue resulting from the garbage cans that they store in the garage.  During the heat of the summer, they have to leave the garbage cans outside because the house starts to stink like garbage.  Same thing going on here: the duct leakage is drawing the odors from the garbage cans into the system and dispersing it throughout the house.  I’m very hopeful that sealing up the return side of this system will fix that problem.
-          2.  Return air temperature.  My father guesses that the garage gets to around 110-120F on hot days in the summer.  Similar to an attic AHU with leaky return ducts, the hot garage air raises the return air temperature and strains the system.  This leads to increased consumption, and energy savings will result from the sealing of these returns.
-          3.  Supply leakage.  The slot for the evaporative cooler component was just blowing conditioned air into the garage.  Sealing this will direct the conditioned air into the home, where it belongs, and will in the process reduce consumption.

On top of this, the duct sealing should help balance out the distribution throughout the home.  Imbalances owing to duct leakage can drive air infiltration across the envelope.  As such, the duct sealing process should also contribute to reduced air changes.

Essential to any duct sealing package is the performing of a post-work airflow test.  Tighter ducts will operate under increased static pressures and, and with this potentially reduced system airflow rates.  Airflow rates too low, and you can freeze up the cooling coil.  I wasn’t real worried about it at my parents house because, although the air handler and plenum are now considerably tighter, the rest of the duct work in the house is still pretty leaky, and I don’t think we came anywhere close to creating static pressures that will reduce airflow to problematic levels.

The lesson, as always: seal your ducts if your house smells like garbage.

Monday, January 16, 2012

Pressurization in High Rise Buildings

Long time, no post.  Here you go.....

The following are a few good articles on building pressurization and stack effect issues in high rise buildings. Uncontrolled air infiltration is the driver of some of the most significant energy waste in tall buildings.  Both horizontal and vertical airflow networks, even ones that are entirely within the building envelope, promote pressure-induced air infiltration and IAQ issues.  Properly sealing and compartmentalizing a tall building can diminish this effect.  

Here is a sketch of some of the airflow networks:


These articles detail the problem, with some recommended fixes.  Like most issues, if care is taken at the design/construction phase, these issues can be made insignificant from the beginning.  High rise buildings have such complex "3-dimensional airflow networks" that it can be difficult to get control over.  If control can be gained, however, IAQ and energy benefits will follow.

For your reading pleasure:

Sunday, January 1, 2012

Bathroom Building Science

Weird title on this one, huh?  Well, this idea developed organically after taking a shower one morning.

In September, we re-painted our bathroom and changed the color.  Once the weather started to get a little bit colder, I started to notice that, after every shower, we had visible streaks of water droplets on two sections of the wall, opposite the shower.  I am sure that this was happening previously, I had just never seen it until we changed the color of the paint on the wall.



I didn't really pay much attention to it.  I'm groggy in the morning, saw the streaks on the wall, and never really thought much about it.  Then one day....EUREKA!  Building science in action.....

The water streak marks are happening at only two places: on the interior wall directly behind the water closet, and on the exterior wall at the ceiling/wall connection.  Why are these the only two places that we are getting this condition?  Once I finally thought about it for a moment, it was pretty clear: the two areas where the streaks appear are condensing surfaces.  After a shower, the ambient air in the bathroom, with extremely high relative humidity, comes in contact with these surfaces.  Water vapor touches the cold wall and condenses into liquid water, which then runs down the wall and leaves the streaks.  Pretty simple.  But why was it happening only at these two locations?

The exterior ceiling/wall connection is fairly obvious.  This area is a pretty typical thermal weakness.  A infrared scan showed that the attic insulation is pulled back directly above this location.  Both the exterior top plate and the drywall are completely exposed to the attic over an area of about 1 sq ft; exposure to the unconditioned attic space drives surface temperatures to below the dewpoint of the moisture laden post-shower air and you get condensation.

The interior wall is a little trickier.  What we have here is a plumbing penetration for the vent stack rising into the attic within the partition wall stud cavity.  This attic penetration is not air sealed.  Unconditioned attic air is falling down the wall, driving temperatures down and creating the condensing surface.  Cool!

Contributing to this whole scenario is the fact that I don't have an exhaust fan.  Code is satisfied by the presence of an operable double hung window, but who's going to open that when its cold out?

The solutions to these problems would be to air seal and insulate the attic properly, and to install a properly vented exhaust fan.  And, probably, to re-paint.....

Dark spot behind the toilet is cold air that has entered the wall cavity through an un-sealed plumbing penetration in the attic, creating a condensing surface.


Poorly installed attic insulation creates a cold spot and the condensing surface.
The cause and solution to our interior wall condensation problem.