Friday, June 6, 2014

Video about Architects for UNICEF Projects in Rwanda

Active Social Architecture (ASA) are architects for the pre-primary schools and early childhood development centers I've been managing for UNICEF. As part of an exhibit in Milan, they had this video made. The videographer only had a few days to shoot, none of the ECDs were complete yet, weather was bad, and they didn't get UNICEF permission (which is why they're not mentioned), but the video is really good. Shows off construction techniques in rural Rwanda. Brick masonry buildings with corrugated metal (pre-primary) or clay tile (ECD) roofs. I'm in the background a couple of times.


Video by What Took You So Long:  https://vimeo.com/89417328 


Thursday, June 5, 2014

PBH Weatherization Project

Back in 2010 I lead a project to work with Harvard students to weatherize the Philips Brooks House. It was a great project with over 50 students attending (including the woman who is now my wife, a post-doc at HSPH at the time) and lots of energy saved. The case study won AASHE's first Campus and Student Sustainability Award for “Best Campus Case Study”. Before the big day, I reached out to Jim Merchant of Pirates Lane (http://pirateslane.com/) who agreed to attend and prepare a video. While looking for something else today I ran across the video and was saddened to see that it had far fewer views than my last cat video (our cat Magilla Glub Glub has a Facebook page). Anyway, with that in mind, I'm sharing the case study and link to the video here. Special thanks to the Green Building Services team for all of their work before, during and after the event. Enjoy.

Case Study on AASHE site:
http://www.aashe.org/resources/case-studies/phillips-brooks-house-student-weatherization-project

Video (about 10 minutes long):
https://www.youtube.com/watch?v=YftpU-fkahU


Phillips Brooks House Student Weatherization Project


Institution(s)

Harvard University

Author(s)

Nathan Gauthier, Assistant Director, Office for Sustainability, Harvard University
       

Project Overview

On May 2nd, more than 50 Harvard students took a break from studying for finals and picked up caulk guns to help improve the energy efficiency of the Phillips Brooks House in Harvard Yard. The project was a collaboration between the Office for Sustainability, the Phillips Brooks House Association, the student Environmental Action Committee, and the Faculty of Arts and Sciences Green Program. Student labor was used to implement 23 weatherization projects in the building. The project is estimated to save more than 9 tons of CO2 equivalent and nearly $4,000 in utility costs annually.

Background

The project was initiated when students from the Environmental Action Committee (EAC) approached the Office for Sustainability and Faculty of Arts and Sciences Green Program asking if there was a way to involve students in a weatherization project similar to what is done by Cambridge Home Energy Efficiency Team (http://heetma.com/). The OFS team toured the building and identified nearly 40 practical energy conservation measures for the Phillips Brooks House, which is a 12,800 square foot, 100 year old, brick building. OFS then designed a program to work with students and issued a proposal to the FAS Office of Planning and Physical Resources to work with EAC students to plan and execute a student-lead weatherization event that would significantly improve the building's performance while engaging students in the process.

Project Goals

The primary goal of the project was to engage students and help them feel empowered to make a positive change on their campus. OFS and FAS wanted students to feel vested in the University's greenhouse gas reduction goal and to encourage them to do their part. The students wanted to have their contributions acknowledged and be exposed to the nuances of building operations and the details around how buildings operate and what opportunities exist to improve building performance. Additional goals included reducing the greenhouse gas emissions and operations costs of the Phillips Brooks House. An added benefit was receiving positive press highlighting student and administrative collaboration.

Project Implementation

Of the nearly 40 energy conservation measures identified for the building, more than 20 were selected on the basis that they could be safely and effectively implemented with student labor. The OFS and student planning team began weekly meetings to organize the project. OFS coordinated with Environmental Health and Safety on student safety issues, the Office of General Council on liability issues, Human Resources on labor relation issues and negotiating with the trade unions, and Facilities Maintenance Operations to identify technical resources that would be beneficial to project success. Cambridge HEET, a local non-profit that specializes in home weatherizations, was consulted to share lessons learned and to provide pre- and post-project blower door testing.



On the day of the event, participants were organized into 7 teams, each led by an OFS staff member and a student leader who had been trained on their tasks ahead of time. The 50 plus student volunteers were trained on safety protocols, tool use, and how to implement the ECMs and then supervised as they performed the work. Projects included caulking storm windows, installing low-flow plumbing fixtures, replacing lamps with compact fluorescents or low-mercury super T8 linear fluorescents, sealing a chimney, installing door sweeps and door jambs, insulating steam pipes, adding smart power strips on computers and timers on water coolers, installing educational signage, and many others. OFS staff was on hand to take photographs and a local videographer responded to a Craigslist ad asking for a volunteer to make a short film. Two full-time interns from Wentworth Institute of Technology worked with OFS throughout this project including helping lead weatherization groups on the day of the event.

Timeline

The project was on a very aggressive timeline because it needed to be implemented before students left for the summer. Students approached OFS and FAS in the last week of February, 2010. OFS Green Building Services walked the building on March 8 and issued a proposal complete with nearly 40 potential ECM opportunities on March 17th. The proposal assumed almost 200 hours of OFS staff time to complete the project with all of the recommended components. FAS approved the proposal the next day (3/18/10) and the OFS team began planning for the event. On March 23, OFS sent the student organizers a detailed description of the proposed process going forward and asked for contact information for student team leaders for the day of the event, as well as for their recommended date for the event and times for weekly team meetings. On March 26 the student organizers provided much of the information requested, though a date for the event wasn't finalized as we tried to coordinate availability of the building with OFS staff availability and student breaks. Student organizers and OFS began weekly breakfast meetings to go over project details, with FAS Office of Physical Planning and Cambridge HEET attending one meeting each to lend their assistance and get updates. By the first week of April, OFS staff and student leaders began visiting the building to put together detailed lists of materials needed to implement their projects and perform practice runs to ensure everybody knew how to perform the tasks for which they were responsible. On March 24th, OFS lead a larger group of students around the building to review all projects identified, including those identified but not being implemented as part of the student project such as demand control ventilation in the lounge area or variable frequency drives on the heating hot water loop. OFS had completed energy calculations for all projects and costed out the materials needed in order to share this information with the students and help them understand the utility cost and greenhouse gas reduction potential of each measure as well as their cost effectiveness. In the middle of April, May 2nd was selected as the day of the event. This was a Sunday during the reading period prior to exams. Invitations to attend were sent to the environmentally themed students groups on April 15th with an online sign up sheet using Google Docs. Materials were purchased during the last two weeks of April. The project took place on May 2, from 11:00 to 3:00, with OFS arriving at 9:00 to start setting up and staying to 4:00 to clean up. Coffee, juice and pastries were awaiting students at sign in and Veggie Planet rice dishes during the lunch break.

Financing

All funding was provided by the FAS Office of Planning and Physical Resources, paid out of their operating budget.

Annual savings are estimated at $3,750 in annual utility costs. We did not quantify the additional maintenance savings from re-lamping all 250 lamps in the building. None of our projects were expected to have an increased maintenance cost. We also did not try to quantify the improved productivity from staff being more comfortable or the benefits of educating students and how this might influence their behaviors going forward.

The total materials cost for the project was $3,300, of which $2,800 was billed to the FAS with the idea that remaining cost went towards tools that could be reused for future projects and would be paid for by OFS. This material value paid by FAS includes the cost of 7 new storm windows, which was not a project performed by the students but was critical to ensure the students caulking the storm window frames knew that their efforts were not in vain. This value also includes the $500 for lunch and $50 for breakfast. Most materials were purchased through Grainger, with additional materials purchased through Energy Federation Incorporated, Home Trends, Watertown Plumbing Supply, Home Depot, Staples, and Conservation Technology.

OFS staff put in 202 hours of time into the project, 192 of which were billed to FAS because of our not to exceed contract agreement. Facilities Maintenance Operations charged for 6 hours of work to have their plumber and pipe wrapper on-site on the day of the event.
Total project costs were $24,043, most of which was from labor.

Project Results

More than 50 students attended the May 2nd event, in addition to the more than a dozen student group leaders, OFS staff, and the Wentworth Interns. The initial, conservative estimates expected a reduction of 9 metric tons of CO2 equivalent of greenhouse gas emissions and $3,750 in utility costs per year. While full verification of the energy reduction may take a year to assess, the building was given a pre- and post-project blower door test to quantify air leakage. The test showed nearly 1,800 fewer cubic feet of air coming into the building when under pressure after the project, which translates to nearly 180 square inches of gaps in the building envelope that were filled… truly excellent results. The bulk of the benefit will be in the winter, when the significant reduction in infiltration will result in steam savings. Everybody responding to the lessons learned survey indicated that they thought the project was very valuable to students and that they hope it is replicated again next year.

Lessons Learned

After the project, a lessons learned survey was sent out to all of the OFS staff and student organizers. 73% of the respondents felt the project was good (4 / 5) and the remaining 27% felt it was excellent (5/5). All respondents indicated that it was a good project that they would like to see repeated.
There were multiple suggestions about broadening the outreach to include faculty and staff, as there were none at the event. The project would have also benefited from having the date confirmed earlier so the outreach could have been done over a longer period of time. Even with very little notice, more than 50 students attended on a Sunday when studying for finals, which seems to indicate there is a lot of interest in this type of event.

Additional time all around would have made the project go more smoothly and would have also likely reduced the cost to FAS as we had to invest significant and possibly redundant resources in order to get everything done on time. While we were able to successfully execute all 23 projects, we had multiple people working on the same or similar tasks for different projects when some of this could have been streamlined if time allowed.

There were a few minor issues during the event with ECMs that didn't go exactly as expected (pipe insulation not quite fitting, dual flush handles not working with all of the toilets, etc.). If we repeat this project, we'll make sure the dry runs in the weeks leading up to the project are more in-depth and can actually confirm the feasibility and the correct parts for all projects. We'll also make sure to order the parts further in advance. One of the packs of lamps we ordered for the chandeliers didn't have the fixture adapter and we didn't have the extra lamps on hand we were expecting.

Another lesson learned was about the door weather seals and students using the drills. It was hard to drill through the steel kick plate without using the more aggressive drill bits, but it was also really hard for students to stop the drill at the right depth. In the future, we'd like some sort of depth guide on the drill to reduce this over-drilling.

Because the blower door test was a bit of an after-thought, we couldn't get Cambridge HEET out on the day of our event. While they were able to come beforehand and afterwards, in the future we would like students to be able to see the actual test and witness the improvements.

 
The film that was made for us by Pirates Lane Video turned out really nicely and putting an ad on Craigslist for a volunteer videographer worked well. We had more than a dozen people volunteer their services. In the future, we'd like to have an OFS staff walk around with the videographer to make sure he's able to film all of the projects. We would have also liked filming of the predatory planning meetings if possible.

We created educational signage and a poster summarizing all of the projects for the students. These sorts of occupant engagement efforts partnered very well with the more typical energy conservation measures and helped make for a more complete event.

We were able to get reusable cups and glasses from Harvard University Hospitality and Dining Services and used all compostable plates and silverware (with composting bins that the OFS staff took home afterwards and brought back to work on Monday). All of the dishes from Veggie Planet for lunch were vegetarian. A number of students commented on appreciating that we made sure to use sustainable dining practices and this is of course something we'd like to do again in the future. A number of people also mentioned that it might be easier to eat pizza instead of rice dishes while outside working.

There were also comments about the project being more for awareness than energy savings, and it may have been nice to have contractors there actually implementing some of the more significant energy saving opportunities at the same time. We identified another 15 to 20 projects that had good payback and would save significant energy, but would require a professional contractor to implement. It might be worth combining the installation wtih the student work in the future. It is also worth noting that the vast majority of the project costs came from planning the weatherization event and not from the actual materials. Using student labor to thoroughly weatherize a building in this manner does not seem to be the most cost effective way to get the job done assuming you have to pay for the staff time needed for planning. The benefits, of course, go well beyond the immediate energy savings from the ECM projects.

There were a few ECMs that really only allowed a couple of people to work on them at a time. In order to engage more students, we would have needed more team leaders and possibly more tools (such as drills). This was only true for a couple of projects like the plumbing projects or door sweeps, but something to keep in mind. Trying to keep 50 or more students engaged simultaneously requires a lot of advanced planning and a lot of knowledgeable leaders.

A critical lesson to share is that early coordination with all stakeholders is critical and that doing so allowed the project to happen without any last minute concerns or hang ups. It requires motivated student leaders, knowledgeable sustainability staff, and facilities leader willing to invest in this kind of project (thank you Jay Phillips). If coordinated with all parties early, potential obstacles can be identified and solutions suggested.

Everybody involved felt this project was a success and that future projects would be even better. It is difficult to succinctly share all of the lessons learned, but the OFS team is very optimistic that if we were able to do a similar event in the future they'll be even more successful than the first.

Quick Look at Embodied Energy of Two Roof Solutions

A friend who is proposing a vaulted roof made from compressed earth blocks / tiles asked me to take a look at embodied energy between his proposed solution and a typical concrete roof. My response is below. Note the initial roof area, thickness, and materials for both the proposed and typical roof were provided by the friend. It appears that the compressed earthen blocks have significantly less embodied energy compared to a concrete dome solution. Another comparison might be the domed earthen blocks to a flat (less area) concrete roof, but this is not represented below. Let me know if you have any questions. Nathan Gauthier

Here is a summary of your emissions and embodied energy comparisons for the two roof options. The earthen dome option has significantly less embodied CO2 emissions (81% less). See below. All conversion factors come form the Inventory of Carbon and Energy (ICE v2.0) put out by Bath University.

 
Most of your savings comes from the tile roof not having steel reinforcement (very high embodied energy compared to other materials) and the earthen tile roof thickness (150 mm) being much less than the concrete (250 mm). Sand, aggregate and cement have the same CO2 per unit for each roof, but there is more volume / mass in the thicker concrete roof. I had to make a number of assumptions (type of lime, strength of concrete, percent recycled content for steel, etc.) but they don’t have a significant impact. Detailed breakdowns follow:
 

All volume to mass conversions from: http://www.simetric.co.uk/si_materials.htm
 
I didn't have Rwanda-specific emissions data, but sand, water, aggregate will all be collected locally with hand labor (aggregate will be crushed by hand), the earthen blocks are hand pressed (machine originally from South Africa), and concrete, steel, and anything else that is imported will come by truck into Rwanda and probably by boat to Mombasa, Kenya. 
 
 

Monday, April 28, 2014

Quality Control - Fired Brick Masonry

Working on early childhood development centers in Rwanda has had me inspecting a lot of masonry construction. There was very little quality assurance put in place when the projects began, so for the most part it has been regular inspections, identifying mistakes, demolishing parts of walls, and re-building correctly. Going forward, a robust total quality management plan will be introduced form the beginning, complete with minimum qualifications, written instructions and signage, assigned people responsible for quality, checklists (pre-construction, during construction, and post), mock-ups, etc. Here are some of the most common errors.
 
 
This wall shows what is supposed to be a Flemish bond, but the header bricks (the single brick running perpendicular to the wall) are cut. The masons do this because the dimensions are bad / inconsistent. If they put the headers in so they are flush with the outside of the building, then there are large divots on the inside where the brick isn't long enough. Ideally, the bricks would be long enough to be flush on the inside and outside (as long as two brick widths plus mortar). We've asked them to pre-select the longest bricks and use them for headers and then to center the headers so there is a small divot on either side. Once Identified as a problem, I prepared signage to have on sites as a teaching tool / prompt, but more needed to happen at the beginning of construction.
 


Another common mistake is bad grout. We're getting very inconsistent mixes (bricks can often be easily removed from walls after the grout is dry). One reason is nobody uses lime, so it is just a small amount of cement and some very dirty sand (often not river sand and they haven't been washing). Regardless of the mix, instead of 1 cm mortar joints, we're seeing as much as 5 cm. This is partly because of un-skilled / un-trained masons, but also because of bricks with different dimensions than assumed by the architects. The architects have shown every single brick in their drawings and when foremen see a certain number of rows of brick under the window sill with specific dimensions given, they are increasing the amount of mortar per row to get the bricks to the level shown on the plans. Going forward, we need to clarify that the mortar joint dimensions are critical (1 cm) and that heights and number of brick courses shown on the drawings for some items, like window heights, have some flexibility.



 
Finally, the rebar in masonry buttresses and columns is new for most masons and we've seen lots of problems. Ideally, the two rebar are spaced 10 cm apart, centered over the buttress or column, and the bricks are woven between the rebar. We're getting rebar poorly set in the foundation, so getting bricks between them / incorporating them into buttresses is difficult. Often, the masons will push the two rebar together and treat them as one because it is easier to lay brick around, though much less structurally secure. Even when it is pointed out that rebar are in the wrong position within a column foundation, we have seen the masons bend the rebar at the bottom to get them where they should be so the entire column becomes wobbly as there is slack in the rebar (and the grout isn't very sticky). 





Saturday, April 19, 2014

Evaluating Natural Daylight Levels

After visiting one of our new early childhood development sites, we noticed the inside of the stimulation rooms (classrooms) were a little dark. They buildings are supposed to be naturally daylit, but nobody on the design team knew anything about estimating daylight or optimizing the design. Subsequently, I’ve reviewed the design and taken light levels in the field. My initial conclusion was that the light levels in the center of the rooms at the floor level often met or exceeded recommended levels (primarily because the windows extend very low to the floor below typical vision glazing and light reaches this spot from multiple directions), but at 1 meter off the floor and in many of the corners the levels were below recommended levels. The Illuminating Engineers Society (IES) recommends 50 foot candles (500 lux) on the writing surface for schools for visual comfort and productivity. Based on the 4 sites I measured, the levels with full sun are typically:
 
 
20 - 30 FC in centre of room at 1 meter
60 - 80 FC in centre of room at floor
5 - 10 FC on bench in “front” of room

 
With these light levels, activities low to the ground in the center of the room (building is designed for children 0 - 6) will be well lit with daylight on sunny days and most overcast days, but children in the corners of the room will have less light than ideal. While a couple of the sites have electric lights available to help alleviate this condition (two, 13 watt CFLs without a fixture), we should advise teachers in all sites to focus art projects, reading, and other visually sensitive tasks away from the bench area.
 
There are a number of potential ways to improve the lighting levels if doing a re-design, as well as some options to improve levels in the already constructed buildings. We decided to go with painting the interior brick white to improve reflectance. Each site has three stimulation rooms so we painted the two longest walls white from floor to ceiling in two of the rooms at one site and re-did our testing. Light levels were almost double in the painted rooms and significantly improved light levels. All sites have since been painted (some not yet to the ceiling as in the image below). While the bench area is still darker than is ideal, the rooms are much improved as a result. At other sites that are nearing the end of construction, we're going to remove some of the brick vent holes at top of the front wall and replace with a framed, translucent plastic window, which should bring the daylight levels up to recommended levels.
 
The lesson learned in this exercise is that daylight modeling or at least crude daylight factor calculations are critical for buildings intended to be naturally lit.
 
 
Extra info (sent to my supervisor when trying to raise the issue):
 
An easy way to evaluate natural lighting is daylight factor (DF), which is the ratio of outside illuminance over inside illuminance, expressed in per cent. The higher the DF, the more natural light is available in the room.
 
The general rule is a room needs to achieve at least 2% DF to be considered daylit, though this is still considered gloomy and electric lighting is needed most of the day. From 2 to 5% the daylighting is better, but electric lighting is still needed up until 5% for optimal visual comfort.
 
Using the crudest rule of thumb method of estimating daylight factor (DF = 0.1 * Glazing Area / Floor Area), it looks like we would just be above the 2% “daylit” threshold as we get 2.7% DF (13.7 m2 glazing / 50.8 m2 floor). Unfortunately, this is overly optimistic in our case for a number of reason. Daylight factor is the sum of three components: direct lighting component (DC), externally reflected lighting component (ERC), and internally reflected lighting component (IRC) such that DF = DC + ERC + IRC. The rule of thumb metrics assume typical office building values for all variables. There are a few problems with this method as we need to account for:
 
  • Many of the windows and one door are shaded from most direct sunlight by roofs above
  • All of the masonry vent openings are deeper (22 cm) than they are tall (8 cm) so let in no direct sunlight most of the day
  • Most interior surfaces are dark and non-reflective and standard calculations assume partially reflective white ceilings and light colored interiors
 
As a result, most of our windows and openings have 0 direct lighting component because of the overhangs (good for avoiding heat gain, but also less visible light), we have very little externally reflected daylight since there are no surrounding buildings other than the others we’ve built with non-reflective exterior surfaces, and we have little internally reflected lighting as our interior materials (especially the ceiling) are darker and less reflective than a typical office. We do have the benefit of very clear glazing in the windows with higher than typical visual transmittance (VT) and of course no glazing in the ventilation openings.
 
Multiple field measurements on the overcast day in Site A showed a range of 1% to 2% DF in the center at 1 meter and about 2.5% to 5% DF in the center on the floor. DF calculations at other sites were not possible as it needs to be overcast and low enough direct sun levels to not overload the meter, but they confirmed the Site B assessment by showing full sun measurements in line with what was expected. 
 
To get up to the 5% daylight factor for the entire room (suggested target), we’d ideally incorporate a combination of increased opening size, especially up high where the contribution to daylight factor is greater, and lighter and more reflective interior surfaces. Even adding the colored paint in the current rooms has already brightened the space a lot compared to the pre-painted condition. We’ll see the impact of the white walls in Site A. 


Sunday, March 10, 2013

Earthen Ducts Question

EMAIL QUESTION ABOUT EARTHEN DUCTS:
 
Nathan,

My husband and I are designing a modest home in northern Indiana to passive house standards. We have a beautiful building site on a south-facing ridge in the middle of forty acres. Picture a house earth sheltered on three sides and open to the south to incorporate passive solar heating/cooling. We will not need a furnace or AC. What we do need is a well-designed whole house ventilation and dehumidification system. I’ve been researching these topics for over a year.

My conclusion: I want to explore the concept of using an earth tube or tubes to precondition our fresh air intake. If I can build a tube system that will achieve a 50% reduction in moisture load on incoming air in the dog days of summer, then tubes are the way to go. My math is not up to the task of evaluating the design. I’ve been trying to connect with a mechanical engineer who could give advice on the psychrometrics. If I can’t find someone to help me geek out the system variables for our site (tube diameter/length, depth, rate of air flow, pressure) then we will have to go with a purely mechanical system to be on the safe side. And then I will always wonder if we missed a grand opportunity.


EMAIL RESPONSE:

I love the idea of Passivhaus, though haven’t been able to work on any projects yet.  Good luck on the project.
 
Calculating the benefits of earth ducts is probably above my math too (I’m not an engineer).  Not one of the easier systems to analyze – I was expecting something easier J   We recently looked at it for a project in Durban, South Africa and besides calculating the potential energy savings, issues to consider include risk of condensation, fan power, and cost of construction.
 
The ground temperature below a couple of meters is usually around the average annual air temperature for your location.  The ground temperature tends to lag the air temperature by a couple of months and the deeper you go the less the ground temp changes.  Using data from South Bend – Michiana Regional Airport, we get the graph below, showing your ground temperature average is about 50 degrees F, but ranges from 40 to 62 at 13 feet and from 30 to 72 at 1.6 feet (this was all in meters originally – so the units for feet aren’t regular).
 
 
 With enough surface area for incoming air to duct contact, you can eventually get the outdoor air almost to the same point (dry bulb) as the ground temperature.  This means that in September, if your duct was 13 feet below ground, you could get the air to about 60 degrees even if it is 90 F outside.  Conversely, you could get the incoming air as high as 45 degrees (13 foot duct) in February, even if it is 0 degrees outside.  Unfortunately, to change the temperature that much, you need longer duct runs.  Assuming you need about 55 cfm of ventilation (2500 sf x 0.01 cfm/sf + 4 people x 7.5 cfm/person), the graph below shows what percentage of the temperature difference (between earth temperature and outside air temperature) you could make up  with different diameter ducts and different lengths (I assumed square / rectangle ducts).  This says that 20 meters of 0.1 x 0.1 duct would make up 90% of the difference between outdoor air and ground temperature.  For example, when it was 0 degrees outside and 50 degrees in the ground in January, you could make up 45 degrees just from going through the duct.
 
 
 
It doesn’t look like fan power will be that big of a deal for you (if you’re providing 55 cfm), regardless of the distance.  When I looked at the project in Durban we were trying to move 8,000 cfm and the fan power penalty was significant.  It looks like you’d really only need a 1 watt of fan power (though you’ll probably have to get one bigger just because that is what is available).  1 x 365 days / year x 24 hours / day / 1000 Wh / kWh = 8.76 kWh per year (about $0.88 per year in fan energy).  I’m only looking at 55 cfm as the ventilation requirement – this air isn’t meant to heat or cool. 
 
 
 
Finally, the last thing you’d want to consider is condensation.  The psychrometric chart below shows one dot for every hour of a typical year (8,760 dots) in South Bend.
 
 
 
The same chart below shows just the dots for a typical August.  During this month, your ground temperature could be around 60 degrees (assuming 13 feet deep).  During the hour that I’ve highlighted (point 1), the air temperature is about 87 degrees, 70% Rh.  When you cool this down towards 60 degrees, you start to get condensation at about 76 degrees (point 2 – the air is now 100% Rh).  By the time you get to point 3, you will have gone from 0.019 grains of water per pound of air to 0.011, with the water that is no longer in the air condensing out in your ducts.  I honestly don’t know how big of a concern this is, but in a typical air conditioner you’d collect the condensation at a specific point and be able to deal with it.  There may be concern about bacteria if you have standing water running the length of your ducts during the summer.  You wouldn’t have to worry about this in the winter.
 
 
 
That’s all I have for now.  If you have specific questions about your system, I might be able to do the calculations for you.  I made a few assumptions in the calcs above (6 bends in each duct work, turbulent flow, concrete ducts for example) and adapted calculations we already had for a larger commercial system, so if we had a real system and started from scratch the numbers could be tightened up  a bit, but I think this info is close.  Thanks to Alejandra Menchaca, PhD and Director of Operations for the Boston offfice of EA Buildings, who did most of the original calculations for our project in Durban.

Nathan

Wednesday, March 6, 2013

Ground Source Heat Pump Question

EMAIL QUESTION ABOUT HEAT PUMPS
Wed, 6 Mar 2013

Hi Nathan,  I am writing about our house in Lexington which my son and family are living in. He has contacted a firm who is planning to install heat pumps to heat/cool 2 floors of our split 3-level house. It is estimated to cost $20,000 with an interest free loan. I just am somewhat skeptical that heat can be supplied reasonably cheaply with electricity and heat pumps in this climate. I wonder if you are able to send me to appropriate literature or home owners who are using this equipment or perhaps give me your opinion. Sam


RESPONSE

Sam,

I usually think of GSHPs in terms of their coefficient of performance (COP). A good one can get around a COP of 4, meaning for every one unit of energy (electricity) you put in you get 4 units out as heat. According to the 2009 Residential Energy Consumption Survey (http://www.eia.gov/consumption/residential/data/2009/index.cfm?view=consumption#end-use) the average house in Massachusetts uses 65,200,000 Btu of energy on heating per year (652 therms about $652 cost). Since most homes use a regular boiler or furnace of around 80%, I'd estimate they only need 52,192,000 Btu of heat (the other 20% is inefficiencies from the boiler). This is the same energy as 15,296 kWh. To get this from a GSHP with a COP of 4, you'd need 3,824 kWh of electricity (about $382 cost). Conversely, if you provided the same 52 MMBtu of heat with a 95% condensing boiler, you'd use 54,939,000 Btu of natural gas (549 therms and $549 cost). GSHPs will save some energy, but the payback is usually pretty long.

As to whether or not the GSHP will work in Boston, it definitely can. We used a lot at Harvard. I know a guy in Somerville who has one for his house (case study link below). Average ground temperature in Boston is about 50. At shallow depths it ranges between about 30 to 70 (see attached from Logan). The ground temperature usually lags behind the air temperature by a month or two (the coldest months for ground temp are a couple of months behind the coldest air months). Still more efficient than trying to use an air source heat pump where the delta T is greater and less in your favor.

The GSHP will also be more efficient than a typical air conditioner, but the annual air conditioning cost is less than the heating cost. Assume you could save 25% or so on your AC bill (say going from a COP of 3 to 4).

I hope this helps.

Nathan