Tag Archives: energy conservation

Dissecting space conditioning

Our January cold spell along with new data from the 2020 Residential Energy Consumption Survey inspired me to further dissect the issue of space conditioning. When it comes to energy use in a building, space conditioning is the 900 pound gorilla in the room. We reduced our space conditioning load through three steps:

First step: The deep energy retrofit, which significantly reduced our overall energy needs through building envelope improvements among other things. This blog is packed with information on insulation, air sealing, window selection, etc. And you can find a summary post here on steps to reduce your overall energy needs.

Second step: Adding a photovoltaic array to our roof top to cover our remaining energy needs. You can search this blog for “solar” or “photovoltaic” to find detailed information on this step.

Third step: Installing heat pumps (also known as minisplits) for space conditioning. You can find more information by searching this blog for “minisplit” and “heat pump”.

The first step was the heavy lifting, and got us the biggest bang for the buck. In fact, our building’s energy consumption for space conditioning ended up below the national average.

And in monetary terms, cooling our building in 2020 was “free” because of the second step: our photovoltaic roof array which provided the needed electricity. Heating our building was almost free. It cost us $173.40 to heat our 4,500 sf building in 2020.

If you would like to know about the nuts and bolts behind those numbers, keep on reading!

Parsing out space conditioning

I used the solar year 2020 (April 1st, 2020 till March 31, 2021), because it was a twelve month stretch where all our space conditioning needs were covered by our heat pumps (single head minisplits). I separated out the general electrical consumption from the energy used for space conditioning by looking at our electrical use on a monthly basis, plus factoring in data from our home energy monitors. The building’s average monthly electrical consumption for everything but space conditioning was 700 kWh.

Our building’s energy use for the solar year 2020 totaled 13,428 kWh. Assuming the average use of 700 kWh per month, we used an estimated 8,400 kWh during the solar year 2020 without accounting for heating and cooling, which took an estimated 5,028 kWh.

solar year 2020Building (kWh)One household in our building (kWh)
Total energy use13,428 (100%)4,476
General energy use (excluding space conditioning)8,400 (62.5%)2,800
Energy use for space conditioning5,028 (37.5%)1,676

2020 data from the U.S. Energy Information Administration shows that space conditioning consumes 46% of the building’s energy use in 2-4 unit apartment buildings like ours (or 52% on average per U.S. household).

Our deep energy retrofit allowed us to reduce that number from 46% to 37.5%, an estimated 8.5% decrease during the solar year 2020.

We are not talking about how much energy is used here, but how that energy use is distributed across various categories, from space heating to refrigeration and all other.

When comparing the 2020 data to that of 2015, we see that these numbers are fairly constant. They are actually hard to change, particularly in existing buildings, because of long established construction types, materials, and methods.

The fact that we were still able to shrink the percentage of energy going towards space heating and air conditioning by a whopping 8.5% for the solar year 2020 is a testament to the success of step number one: reduction of our overall energy load through building envelope improvements. And it pays off:

In terms of heating cost…

…how did I get to $173.40 to heat our 4,500 sf building for the solar year 2020?

From April through to December we only paid for fixed costs ($12.83/month for customer and meter charges) because our photovoltaic array combined with our net-metering agreement covered our electrical needs. For the last three months of the solar year (January, February and March) we had to purchase electricity and paid a total of $289 for the 2,038 kWh we used.

TotalkWh w/o space conditioningSpace conditioning
Jan 20211,839 kWh minus700 kWh =1,139 kWh
Feb 20212,139 kWh minus700 kWh =1,439 kWh
Mar 20211,254 kW minus700 kWh =554 kWh
Total5,232 kWh (or 100%)3,132 kWh (or 60%)
Total cost$289 (or 100%)$173.40 (or 60%)

Looking at the total kWh consumed and the breakdown between kWh for space conditioning and kWh for everything else, an estimated 60% ($173.40) of that energy went towards space conditioning (heating) our 4,500 sf building with the minisplits for the three months we ran a deficit.

There is nothing mysterious about this, as long as you don’t fall into the trap by starting your project with a heat pump.

Follow the three steps, and numbers like this (or better) can become a reality:

  1. Address thermal deficits in the building envelope first to significantly reduce the overall energy load of the building.
  2. Combine those improvements with a renewable energy project, such as a photovoltaic array, that now has the potential to cover 100% or close to 100% of your energy needs. 
  3. Install an efficient heat pump system that is small and compact due to the reduced overall energy load of your building, and subsequently is largely or entirely powered by your renewable energy system.

But there was something magical about this: We ended up with a very comfortable home!

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How close to net-zero are we?

To answer this question, let’s look at the data for the solar year 2020 when our electrical use included space conditioning.

Our annual use totaled 13,428 kWh that year, while our annual production amounted to 11,390 kWh. The solar array produced enough electricity to cover 85% of our annual consumption.

To reach net-zero, we would need to be at 100% or above. So we are around 15% short of net zero and had some more homework ahead of us.

The moving goal post…

When we embarked on the project in 2009, all-electric homes were not a thing yet, heat pumps were hard to find, and solar arrays were uncommon.

At the time my focus was on using a solar hot water system to heat the building and for domestic hot water, and a photovoltaic array to cover our electrical needs. But I always found myself on thin ice when attempting to cover space heating and domestic hot water with a solar hot water system alone. In other words, getting away without a natural gas connection seemed impossible, which made the net zero goal hard to reach.

I pivoted my focus into significantly reducing the overall energy load of our building. If I had to use natural gas as an energy source, I wanted to use as little as possible. That put us on the path of our deep energy retrofit.

And it paid off.

Interim results in 2012 showed that our improvements reduced our electrical consumption by an estimated 57% and preliminary results from 2016 showed that we reduced our heating needs by an estimated 80%.

A lot has happened since 2009. Green building technologies that once were only known from excotic places like Europe or Asia suddenly made an appearance in the U.S. market, such as heat pumps. And with that, my focus on solar hot water fell away, because heat pumps emerged as a more economic option that I still could use, even if the sun was not shining.

Reducing the general electrical load of a building also has become easier since 2009 with increasingly efficient energy star appliances, LED lighting, etc.

What is standing in the way of net zero?

Yet we are not net zero, to my chagrin. What is standing in the way are two key factors:

  1. That we still rely on natural gas for cooking, domestic hot water, and occasional heating. And we still have a gas dryer.
  2. That our solar array is not large enough to cover 100% of our energy needs should we go all electric.

The second point should be reasonably easy to solve. Because we have reduced the energy load of our building significantly, we have enough room to expand our solar array to cover 100% of our energy use. And we plan on doing so – eventually – once technology catches up.

Regarding the first point – our natural gas connection – it helps to know how much natural gas goes towards what source in our building.

Analyzing our utility bills over the past seven years revealed that about 700 therms (70%) went towards space heating, with only 300 therms (30%) going towards domestic hot water, ranges, and the dryer.

The 300 therms seemed to be easy to solve. We can replace our gas dryer with a condensing dryer. The gas ranges can be replaced with induction stoves. And the heat pump water heater technologies have improved to the point where we could say goodbye to a gas fired water heater too.

As for the 700 therms going into space heating, one could argue that we solved that problem already with the addition of our minisplits. We used them to heat our building during the solar year 2020, and it worked.

But there is a problem: we drank the kool aid.

We originally, and occasionally still rely on our hydronic heating system, powered by a high efficiency boiler. The steel baseboard radiators and radiant floors deliver a comfort during the heating season that is unmatched.

The good news is that we potentially could replace our boiler with an air-to-water heat pump that used CO2 (R744) as a refrigerant. These units are slowly making an appearance in the U.S. market and are able to deliver 130F water even at very low exterior temperatures. 130F would be a suitable temperature for our hydronic heating system and domestic hot water.

Not only that, but an air-to–water heat pump would be two to three times more efficient than our high efficiency boiler. In other words, it would only require half or one third of the energy input to produce the equivalent of 700 therms heating output.

I am hopeful to eventually replace our boiler with an air-to-water heat pump and solve the 700 therms that were needed for space heating.  We subsequently could cut our natural gas supply to the building, and yet still enjoy the comfort of our hydronic heating system.

That must be expensive!

In the big picture, what is the cost of doing nothing?

And on a project basis, if it is expensive depends on one’s mindset.

Most of our system decisions, such as the heating system, were not solely based on the economics of the day, or “what is the cheapest system I can get.” We were comfortable investing in systems with a longer payback period as long as they came with:

  1. a high level of energy efficiency,
  2. some level of resiliency and longevity,
  3. improved indoor comfort and health without an energy penalty, and
  4. systems that were somewhat future-proof so that they could adapt to technology upgrades.

This required a lot of research and careful planning at the onset of our project. And it required a lot of luck, as we were gazing into the future trying to predict the path green building technologies would take.

And in practical terms?

It appears that our utility room layout could accommodate the switch from boiler to air-to-water heat pump without revamping the whole hydronic heating or domestic hot water layout.

And because we were mindful when we installed an all new electrical metallic tubing (EMT) based electrical system, providing 240V for the induction stoves and potentially the condensing dryer should just be a matter of simple rewiring.

The one item that wasn’t even remotely on the radar in 2009, and that I still have to wrap my head around, is how best to integrate and accommodate EV charging stations.

In summary: We are not net-zero yet. We are fairly close, and we know the path that will take us there.

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Renewables

We reached the point in our Chicago deep-energy-retrofit where we get to work on the renewable energy component: a solar electric system in our case. Needless to say that we are super excited.

The topic of renewable energy generally creates a lot of excitement and buzz. So let me throw in a word of caution:

If you are on a path to make your home more energy efficient, the renewable energy component should be at the very end of your list. First take steps to reduce the overall energy demand of your home, because this is where you get the biggest return on your investment.

A general rule of thumb that I have come across says: every $1 spent to improve the efficiency of a structure saves $3 to $5 on the cost of a renewable energy system. That said, I did not find any research that backs up this claim.

Nevertheless, it rings probable: I did an initial performance analysis back in 2012 and 2016. I took energy data of a building comparable to ours prior to any energy improvements and compared it to our energy usage. I converted both data sets to a square foot basis to get an apples to apples comparison.

By 2016 we had reduced our heating load by 80%, while our electrical consumption decreased by 57%. And keep in mind that we were still working on the building, meaning that there still were lingering inefficiencies.

The bottom line is a renewable energy system for our house would be 1/2 to 1/4 the size of what it would have been prior to any energy improvements. This translates into major cost savings.

And then there are spatial limitations to keep in mind.

Take a solar energy system, i.e. photovoltaic panels in an urban setting. The panels are typically mounted on the roof. But any given residential roof can only accommodate so many photovoltaic panels.

The lower the energy use of a home, the more likely that the panels on the roof cover the majority, if not all of the energy needs, which again translates into major cost savings.

How do you improve the energy efficiency of your home? I provided some guidelines in the previous post. But there is plenty of more information in this blog. Just search the blog for keywords like “building shell”, “insulation”, “air sealing”, “windows”, “heating”, “space conditioning”, “moisture management”, and “ventilation” and you will find plenty of reading material on energy efficiency strategies.

Ok, the “word of caution” turned into several paragraphs. In the next posts, I will get into the basics of solar PV and our journey to the system installed, including all preparations. Stay tuned!

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How do I start…

… with energy improvements on my home?

This is probably the question I get most often.

Whether you are thinking about smaller improvements or bigger ones, like our deep energy retrofit, here are some guidelines on how to go about it.

The big picture

It is not just about energy improvements, but it is also about where you get the biggest bang for your buck. So let’s take a look at the big picture.

For more data go to: https://www.eia.gov/consumption/

The 2020 chart above from the U.S. Energy Information Administration shows that up to 54% of energy for a single family home can go towards space conditioning (i.e. space heating and cooling). Only 5% of energy goes towards lighting.

If you decide to make your lighting more efficient, i.e. go with all Energy Star LED lighting, I applaud you. However, the total resulting energy savings may be around 1-2%. That’s something you may barely notice on your electrical bill.

If instead you would focus on improvements to your building envelope, i.e. your basement floor, foundation walls, crawlspace, exterior walls, wall penetrations, windows, exterior doors, attic, and roof, you could make a major dent in the 54% of energy that goes towards your space conditioning. This is where you can get a big bang for your buck. And not only that, you likely end up with a home that is a whole lot less drafty and a whole lot more comfortable and healthy to live in.

The bottom line is, don’t focus on the low hanging fruit. Look at the big picture and focus on the energy hogs, such as space conditioning.

Verify and quantify

You decided to not just chip away at your energy use but instead to make a dent, maybe even a really big dent.

Based on the data above, you know that you likely need to focus on your building envelope in order to reduce your space conditioning loads. But how good or bad is your building envelope, and what is the actual space conditioning load for your home?

It’s time to find out. Commission a home energy audit. A professional energy auditor will visit and inspect your home, analyze your utility bills, and may run several tests such as a duct, furnace, and blower door test.

For more information on home energy audits go to: https://www.energy.gov/energysaver/home-energy-audits/professional-home-energy-audits

The energy audit report will point you to the areas where energy improvements can be most effective. The most significant recommendations will probably point you to building envelope improvements, such as insulating, air sealing, door or window replacement, etc.

With this data and recommendations in hand, you can begin to strategize.

Weatherization

You have a choice. Even basic insulation along with good air sealing (also called home weatherization) can save you an “average of 15% on heating and cooling costs (or an average of 11% on total energy costs)” according to Energy Star information.

For more information go to: https://www.energy.gov/energysaver/weatherize/air-sealing-your-home

Depending on how handy you are, weatherization can become a DIY project or you can hire a weatherization specialist that does the air sealing and insulating for you. If you hire someone, make sure that you contractually set performance goals based on the home energy audit. This means how much more air tight the house should be after the improvements and what cold spots should be eliminated with insulation. And at the end, go and verify. In other words, have your energy auditor come back to test that the performance goals are met.

Energy model

You want to aim higher and save more? Good for you!

In this case I recommend commissioning an energy model, which your home energy auditor could provide. And if not, he or she can probably recommend someone. We commissioned an energy model in the planning phase of our project, which guided us through the decision making process.

An energy model takes a wide variety of building variables into account (type of windows, type of insulation, building exposure, air tightness, etc.) and predicts the energy load of your home. By adjusting the variables (i.e. thickness of insulation, type of windows, level of airtightness, etc.) you can see how the energy load of your home increases or decreases.

Say you want to decrease the energy load of your home by 50% or more, which puts you into the realm of deep energy retrofits. The energy model will help you to determine how to get there. It tells you what level of air tightness you need to achieve. It tells you what levels of insulation values you need, and where. It tells you what performance targets your windows and exterior doors should meet. And so on.

Decreasing your energy by 50% or more will involve major remodeling as you probably have to work on all exterior walls and the roof from the inside, the outside, or both.

Sounds daunting? Well, it can be. But there are silver linings here too.

Major remodeling allows you to get to all those quick fixes and deferred maintenance items that have been causing problems and eating money for years. And of course, you are left with major energy savings.

Take our deep energy retrofit. A preliminary analysis in 2016 showed a 80% reduction in our heating needs, and 57% reduction in our electrical use in 2012.

Be picky with your contractors

You will need help from various building trades with a deep energy retrofit. I highly recommend relying on contractors that specialize in energy improvements, or that are at least familiar with the topic. Working on energy improvements, such as in a deep energy retrofit, takes a very different mind set compared to regular construction, as the installation and construction processes often vary from the old norm. A recipe for disaster is a contractor that is set in the old ways, because that is how he/she has always done it.

Don’t tiptoe

Aiming high, such as with a deep energy retrofit, may seem expensive and overwhelming. You may think you should start in small increments instead.

Please think again.

Going about your improvements incrementally, each step in the process seems less overwhelming and less expensive. I’ll give you that. However you keep tiptoeing around big ticket items and associated savings (such as the above mentioned space conditioning). And you will likely end up undoing some of your own work along the process.

In the end, you may have spent cumulatively more on incremental improvements than on a deep energy retrofit with far less energy savings than you would have had if you didn’t tiptoe..

Learn how to operate your home

Owning a home, energy efficient or not, requires you to know how to operate it.

It is similar to owning a car: If you want to drive, you need to know how to start your car, how to steer it, how to accelerate and brake. You need to know what kind of gas you need, how to put gas in the tank, check tire pressure, check oil levels, etc.

The same is true for a home, in particular if you like to maximize your energy savings. You need to know when to change or clean which filters and when to schedule service appointments for what equipment. You will have to program and monitor your thermostat and other monitoring equipment. You should become familiar with the basics of indoor air quality (IAQ) and learn the basics about moisture management.

Owning a home is not a hands-off operation! There is no chauffeur. You need to drive if you intend to maximize your energy savings, assure the durability of your home and systems, and maintain a healthy and affordable living space.

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Establishing electricity

I kept busy at the U.S. Green Building Conference and Expo, which was in town. While I was cruising the tradeshow floor looking for the latest developments in sustainable technologies, a young man walked up to me and said: “You are behind on your blog.”

Was I surprised? Hell yes! Did I get the hint? Let’s say yes to that one too.

Two weeks ago I talked about the service desert. The subject for today is about another service, the electrical main service.

temp-elec-01

The old main service into the house was a 100 amp line feeding three meters and subsequently three breaker panels in the basement.

The wiring in the panels was – let’s say – creative, and not necessarily safe. I had everything disconnected relatively early on. Later on, Cathy discovered the wire that was not running through the meters or breakers, but came directly from the main service.

electrical-main-service-01It’s time to replace the existing setup with a new main service to a bank with four meters (garden unit, 1st floor, 2nd floor and public areas) and new breaker panels.

There was some confusion to whether we need a 200 amp or 400 amp main service to the meters. The electrician recommended a 400 amp main service for three 100 amp panels and one 60 amp panel for the public areas (totaling 360 amp).

The design documents specified a 200 amp main service, as it is highly improbable that the users in all three units would ever get enough appliances going to get close to a 360 amp load. This is particularly true since our goal is that of energy efficiency and conservation.

The case was quickly settled by the building inspector, who has the last say in these things. I learned that 100 or 200 amp service to buildings like ours is typical. If anyone would like to install a main service larger than 200 amp, the building department requires a load schedule that lists all points of electrical use for each unit and their estimated electrical load.

With that clarification at hand and our goal of minimizing our electricity consumption we eventually got the 200 amp main service installed.

Moving on into the basement, we have the panel for the garden unit and the public circuits located right behind the electrical meters on the outside.

electrical-main-service-02

The other two panels are placed on the 1st and 2nd floor for easy and convenient maintenance access.

electrical-main-service-03 electrical-main-service-04

This layout does require us to install two disconnects to the 1st and 2nd floor in the basement (see image above).

We now have established electricity to the breaker panels. The next step is to run conduit and cables through each unit.