Category Archives: Equipment Size

Why The Way your AC is installed Matters! Part I

Screen Shot 2016-06-24 at 8.49.56 AMThe Air Conditioning Contractors of America (ACCA) publishes ANSI Standards for HVAC Contractors to follow. These professional standards are well known in the Home Performance Industry and the HVAC Contractors.  I found a link on their website this morning to a study showing the problems caused with problems that can easily occur if the Industry Professional Standards are not followed.

I covered a study from California about these types of faults recently. This one was completed by NIST.  The National Institute of Standards and Technology, a part of the US Department of Commerce.

CookA quick review of the reports shows many technical details and mathematical formulae.  That forms the back ground for comparisons with other studies.  However, they did write in some plain English for the rest of us. Here is one of their findings, about the performance of heat pumps.

A Heat Pump provides both heat and air conditioning. It is efficient because it moves heat.  In the summer, it moves heat from inside to outside, just like an ac unit.  The same technology and principals. In the winter they move heat from outside to inside. Yes, there is heat outside at cold temperatures.

Think about your refrigerator. When it gets up to around 40° F inside, the unit turns on and finds the heat in that 40° temperature and moves it out of the refrigerator to keep your food cool and fresh. If you watch your temperatures outside, you know more heating is done at 40° and above than at 20°.

This findings for a heat pump cooling your home apply to geothermal heat pumps, regular heat pumps and to air conditioners. They are all working on the same principals.

The first fault they report on is having the wrong size unit.

Changing the size of the heat pump for a given house – either undersizing or oversizing – impacts the heat pump performance in several ways:

  • Cycling losses increase as the unit gets larger; the unit runs for shorter periods and the degraded performance at startup has more impact (parameters used in simulations are: time constant = 45 seconds, or CD ~ 0.15).
  • In the cooling mode, the shorter run periods impact the moisture removal capability (i.e., ability to control indoor humidity levels) because operational steady-state conditions are an even smaller portion of the runtime fraction.
  • In the cooling mode, continuous fan operation with compressor cycling greatly increases moisture evaporation from the cooling coil. However, this impact is minimal with auto fan control (indoor fan time ‘on’ and ‘off’ the same as that of the compressor), since only a small amount of evaporation occurs with the assumed 4 % airflow during the off-cycle with the indoor fan off. If the air conditioner controls include an off-cycle fan delay – that keeps the fan on for 30-90 seconds after the compressor stops – then the impact of off-cycle evaporation is in between these two extremes (Shirey et al., 2006). The results in this study assumed auto fan operation with no fan delay.
  • Heat pump sizing also affects the level of duct losses.

A improperly sized unit will run for shorter periods, and will turn on and off more often. That is just like driving your car around downtown Wichita. Lots of stop lights. Compare you gas mileage to highway driving at a steady speed of 55 mph or higher.

OK, I know efficiency isn’t as important as being comfortable. So the next item is the comfort side.  Running you AC like your car in Down Town, doesn’t remove the humidity as well. Your house temperature is cool, but the humidity is high and you turn down the thermostat again to get rid of the humidity. Pretty soon you are cold, and yet you are not comfortable because you feel the high humidity.  Then you go out and buy a de-humidifier.

The third item is also a comfort issue. That is the advice of many HVAC technicians to set your AC fan to run continuously. When the AC shuts off and the fan keeps running, the humidity the AC just removed from your house is put back in. Oops!

DadBabyESFinally the report mentions duct losses. They are important in a home that has no basement. In those homes ducts can be located in the attic or the crawl space, or both. If you have one of those houses, I would be glad to address that one in the comments. So leave a comment if your are interested.

How do you get a right sized AC unit?   Your HVAC contractor can run a series of calculation found in the professional standard from ACCA Manual J.  It is a Load Calculation.  For cooling it considers the insulation in your home, the windows and size of the home and other details. It can be done on a paper worksheet or a spreadsheet. Both are free from ACCA. Most contractors have a software program to run these Load Calculations.

Load calculations for cooling, are a balancing act. The homeowner wants a home that is cool in the summer and in Wichita, they want the humidity controlled.  Without a lot of formulae or detail, how do, the rest of us, understand a cooling Load Calculation?

My advice is to look at the out door design conditions that must be factored into the calculation.  For cooling, ACCA Manual J has 6 outdoor conditions.

  • Two relate to location. Cooling in Atlanta, is different from Wichita and is different from Denver.
  • One is the outside temperature. The choice is a temperature that covers all but 1% of the hours in a year that require cooling for that location.
  • There are four design conditions that relate to Relative Humidity.

This obviously requires a balance. If your contractor varies from these conditions, it still must balance.  You may or may not like the balance, if one item is changed without consideration of the others.

What should you as a consumer do?

Insist that professional standards be used.

Require that all the items of the standard be measured and reported.

For Air Conditioning the standards require measurements of:

  • Air Flow Actual compared to manufacturer’s requirements. (+/- 15%)
  • Air Flow Static Pressure (ESP)  Actual within the manufacturer’s acceptable range
    • AND
  • No more than 25% or 0.10 IWC over the design pressure for the duct system.
  • Refrigerant Charge Verification
    • Superheat method:  Within +/- 5% of manufacturers superheat value.
    • Sub cooling method: Within =/- 3% of the manufacturers subcooling value.
  • Measured line voltage and low voltage circuits for voltage and amperage. These values shall be within the manufacturer’s requirements.

If you have good air flow in some rooms and not enough air flow in other rooms, your home has an air balancing problem. Have your system checked and balanced. This is known as test and balance or TAB. I have done test and balance work. Generally, the air flows should be within 20% of the design or application requirements.

Using One HVAC System for Two Areas

My first audit was triggered by the homeowner concerned that the upstairs was several degrees warmer than downstairs. Since we all have experienced Hot Air  goes up, it makes some sense.  In this case the difference was 15° F at 8:00 am, rising to 20° F by noon that August morning.  Yes, it was hot.

4 square craftsmanThere are a number of ways to help this out, for existing homes. Which one is best depends on the specific home, the existing setup and the homeowner.  For new homes, it usually falls to the HVAC guys to work out.

In a new 2 story home, it is common to see two HVAC units.  One in the basement for most of the home and one in the attic for the second floor.  Some builders, concerned with cost, or space considerations, will try a Zoned System.  You can also find Zoned Systems in single story homes, with the master suite on one zone and the rest of the home on another zone.

furnace bypass zoneTypically, the set up uses a bypass and several dampers to control the air.  The wisdom of this approach is that changing the air flow through the unit costs a lot of $$$$.

In the video below, John Proctor, goes through the measurements and calculations of using or not using a bypass and dampers to figure out exactly what is happening.  His conclusion:  The Bypass Damper set up costs 22% – 32% more.

This video is primarily written for HVAC contractors and others interested in the details and workings of air conditioning.  If all the numbers make your eyes glaze over, that is OK.  All you want is comfort, a Bypass dampened system may do that at a cost. It may have the cost and not do that.  So if you are considering a Zoned HVAC system,  tell your contractor —  ‘No Bypass Dampers’!  And refer them to this post.

What % Of The Cost of a New Home Cost, Does The HVAC System provide? 5%, 10% ,15%???

This question was raised this morning on one of the professional discussion forums. Below is my response. Included is a link supplied by Richard McGrath in another response.

Let’s use a water bucket and a faucet for an analogy.

Take a page from the British Navy a few hundred years ago. They learned to tar the joints of their wooden hulled ships. Perhaps that’s why British Seamen are called ‘Tars’.

taringshipIf you build your bucket with wood, you do something to stop the leaks. To use the bucket, you have a faucet to put water into it. If you put less money into the bucket stopping the water loss, you will need to put more water into it all the time, and need a larger capacity faucet. That will cost more money. The reverse is also true.

The question is ‘what should our faucet cost’? Most people would look at it and say not much! For a half million dollar house you might get answers from 2-4%. Some would say less. A faucet system is not just the part you see sticking out of the wall? The system includes pipe from the source of water to the house, to the various rooms where water is needed. You can’t buy a $10 faucet and claim to have a faucet system.

For this question, you can’t buy a furnace and AC unit and claim that is the system. You must have a Thermostat and some way to get the heat and cool to the various rooms of the home. For an effective faucet system, you put some thought and effort into the design. The same goes for an HVAC system.

What is the bucket in our house? Sometimes it is called the thermal envelope, sometimes Thermal Enclosure. It is formed by a continuous thermal boundary that is aligned with a continuous air barrier. Pretty simple in concept, Not as easy to execute. Put some time and effort into the design; then put some effort into the execution.

Choose your insulation types and amounts carefully.  Each have advantages and disadvantages. Air seal the building. All fibrous insulation types allow air to flow. That flow will decrease or eliminate the value of the insulation.

Properly flash and seal the openings for windows and doors. Specify the U-factor and SHGC for the windows. Calculate the correct overhang for the eaves. You want to have them cast a shadow over the whole window at noon on June 21st.

Properly air seal the home. Install your WRB (water resistant barrier) correctly. That means following manufacturer’s directions. Wrap types mean gasketed nails, properly lapped and taped with approved products. You can use factory applied WRB to the OSB or a site applied liquid to the house. Air sealing doesn’t stop there. Fill each 1 inch hole the electrician drilled with caulk or foam, most wires running through those holes are about 1/2 inch. Then seal the joints of the wall and ceiling drywall on the attic side. Caulk or froth pac work. You can flash 1 inch of CC SPF also.

Now your house, bucket, is not very leaky. So you don’t need a big faucet. Big faucets relate to size of the HVAC system, they also directly relate to the cost to install. You also have the cost to operate.

After you have a well built air leakage controlled envelope, then you can consider the HVAC system. ??Two choices to start with: Hydronic or Forced Air. Forced air is most common in this area, we will persue that route.

After choosing Forced Air, you can choose gas fired heat or an electrically driven heat source. Again 2 choices. ??With a gas fired heat source you will have conditioned air leaving the ducts at 100 – 110° F. With an electrically driven source the air will leave the ducts at 85 – 95° F noticeably cooler. That will make or break many people on their choice and ultimate satisfaction with their HVAC system.

Gas fired comes in primarily Natural Gas and Propane. Availability is the key here. ??If you choose a gas fired system – go sealed combustion on the furnace and either sealed combustion or fan assisted drafting on the DHW.

If you choose to go with an electrically driven system, you can choose a Heat Pump or an electric furnace. If you choose an electric furnace, IMO you will not be pleased with your operating costs. They will be through the roof and you will invest any capital cost savings in operating costs very quickly.

That leaves a heat pump with Two Choices. You can choose an Air Source or a Ground Source. ??With a well designed and built duct system, meeting the standards for leakage and design for the Energy Star 3.0 program; a ASHP with variable speed ECM motor (which may be overkill) including actual Manual J, S, and D work ups around here will cost between 9 – 15 K. A gas fired system will be very similar in price, as would a dual fuel system.

If you opt for a typical closed loop Ground Source set up, including all of the above, wells and piping your capital cost will run between 25 – 35K. (noted for the next 27 months a 30% tax credit is available, but not considered in this article.)

In this area new construction homes range from 125,000 to 7 million. ??So the lower end is in the 7 – 12 % range. The more reasonable price of 500,000 for a high end spec home in the area results in the 3 – 7% range.

The question of percentages is silly. Builders may like them, but most homeowners will have their eyes glaze over if you bring this up. The goal is to sell homes, not HVAC systems. A home is supposed to be comfortable. Many new ones are not. This link goes into depth on this issue. http://www.healthyheating.com/Thermal_Comfort_Working_Copy/comfort.htm#.Uj9kLr7D_5o

The equation of importance is capital cost to operating cost. Those are best approached with some modeling. I recently completed a model for a 3K sf home with R-25 ICF V 2×4 16OC construction. The operating costs were in the $1,500 range for our utility rates. The HERS Score was 54.

Substituting a GSHP brought the operating costs down by $200 per year and increase the capital costs by 10K. ??The customer opted for the ASHP and ICF over the GSHP and typical construction. He chose where to put his money.

I see a trap in logic using percentages. I provided new construction pricing around here. My cousin in California deals with homes on the bottom range in the neighborhood of 500,000. That makes a hugh difference in the % equation. So try rephrasing the question to get some more accurate results. Leave out the percentages.

The Energy Guy Does Rounding For 3rd Graders

I was recently asked to make a short video for children 8 – 9 years old. The subject was to involve how I use rounding in my job.

I chose to use measuring a house to obtain the size in cubic feet and relate that to choosing the size of the furnace. I varied the measurement on each side of the house by 6 inches.  The measurement rounding was shown to be accurate enough for this need. In this case the accuracy requirement was not needed due to furnace engineering issues, not the ability of someone to measure to the nearest inch or 6 inches.

Enjoy the video – help some kids! Thanks to the Third Grade Teacher, Grace for including me.  Here is the video on my You Tube Channel

http://youtu.be/xhZvH4RLY6U

How Accurate is your Tape Measure, an Example of Rounding for Third Graders

I was recently asked to make a video for a 3rd Grade Teacher on how I use rounding in my job.  This is a great subject.  My wife is a math teacher and has helped teach estimating and rounding to Grade School children for years.

I chose to use measuring a house to obtain the size in cubic feet and relate that to choosing the size of the furnace. I varied the measurement on each side of the house by 6 inches.  The measurement rounding was shown to be accurate enough for this need. In this case the accuracy requirement was not needed due to furnace engineering issues, not the ability of someone to measure to the nearest inch or 6 inches.

Enjoy the video – help some kids! Thanks to the Third Grade Teacher, Grace for including me.  Here is the video on my You Tube Channel

 

http://youtu.be/xhZvH4RLY6U

What percentage of residential new construction cost do you think a high efficiency HVAC system should be? 5%, 10% ,15%???

This question was raised this morning on one of the professional discussion forums. Below is my response. Included is a link supplied by Richard McGrath in another response.

Let’s use a water bucket and a faucet for an analogy.

Take a page from the British Navy a few hundred years ago. They learned to tar the joints of their wooden hulled ships. Perhaps that’s why British Seamen are called ‘Tars’.

If you build your bucket with wood, you do something to stop the leaks. To use the bucket, you have a faucet to put water into it. If you put less money into the bucket stopping the water loss, you will need to put more water into it all the time, and need a larger capacity faucet. That will cost more money. The reverse is also true.

The question is ‘what should our faucet cost’? Most people would look at it and say not much! For a half million dollar house you might get answers from 2-4%. Some would say less. ??A faucet system is not just the part you see sticking out of the wall? The system includes pipe from the source of water to the house, to the various rooms where water is needed. You can’t buy a $10 faucet and claim to have a faucet system.

For this question, you can’t buy a furnace and AC unit and claim that is the system. You must have a Thermostat and some way to get the heat and cool to the various rooms of the home. For an effective faucet system, you put some thought and effort into the design. The same goes for an HVAC system.

What is the bucket in our house? Sometimes it is called the thermal envelope, sometimes Thermal Enclosure. It is formed by a continuous thermal boundary that is aligned with a continuous air barrier. ??Pretty simple in concept, Not as easy to execute. ??Put some time and effort into the design; then put some effort into the execution. If you are building with 2x4s use 24 inch centers, ladder connections for interior walls and 2 stud corners. Fill the extra room with insulation not wood. NAHB pioneered this in the 1970’s because of the high cost of framing material. ??You can install R-13 batts in those 2×4 walls, or you can use a blown in system. If you get the correct density and verify it, you can get R-15. You can choose a hybrid system with a 1 inch flash of CC SPF and blown in FG or Wet Sprayed Cellulose. R-17 or 18. ??Insulate the basement walls, crawl space walls and the above ground walls. ??Properly flash and seal the openings for windows and doors. Specify the U-factor and SHGC for the windows. Calculate the correct overhang for the eaves. You want to have them cast a shadow over the whole window at noon on June 21st.

Properly air seal the home. Install your WRB (water resistant barrier) correctly. That means following manufacturer’s directions. Wrap types mean gasketed nails, properly lapped and taped with approved products. You can use factory applied WRB to the OSB or a site applied liquid to the house. ??Air sealing doesn’t stop there. Fill each 1 inch hole the electrician drilled with caulk or foam, most wires running through those holes are about 1/2 inch. ??Then seal the joints of the wall and ceiling drywall on the attic side. Caulk or froth pac work. You can flash 1 inch of CC SPF also.

Now your house, bucket, is not very leaky. So you don’t need a big faucet. ??Big faucets relate to size of the HVAC system, they also directly relate to the cost to install. You also have the cost to operate.

After you have a well built air leakage controlled envelope, then you can consider the HVAC system. ??Two choices to start with: Hydronic or Forced Air. Forced air is most common in this area, we will persue that route.

After choosing Forced Air, you can choose gas fired heat or an electrically driven heat source. Again 2 choices. ??With a gas fired heat source you will have conditioned air leaving the ducts at 100 – 110° F. With an electrically driven source the air will leave the ducts at 85 – 95° F noticeably cooler. That will make or break many people on their choice and ultimate satisfaction with their HVAC system.

Gas fired comes in primarily Natural Gas and Propane. Availability is the key here. ??If you choose a gas fired system – go sealed combustion on the furnace and either sealed combustion or fan assisted drafting on the DHW.

If you choose to go with an electrically driven system, you can choose a Heat Pump or an electric furnace. If you choose an electric furnace, IMO you will not be pleased with your operating costs. They will be through the roof and you will invest any capital cost savings in operating costs very quickly.

That leaves a heat pump with Two Choices. You can choose an Air Source or a Ground Source. ??With a well designed and built duct system, meeting the standards for leakage and design for the Energy Star 3.0 program; a ASHP with variable speed ECM motor (which may be overkill) including actual Manual J, S, and D work ups around here will cost between 9 – 15 K. A gas fired system will be very similar in price, as would a dual fuel system.

If you opt for a typical closed loop Ground Source set up, including all of the above, wells and piping your capital cost will run between 25 – 35K. (noted for the next 27 months a 30% tax credit is available, but not considered in this article.)

In this area new construction homes range from 125,000 to 7 million. ??So the lower end is in the 7 – 12 % range. The more reasonable price of 500,000 for a high end spec home in the area results in the 3 – 7% range.

The question of percentages is silly. Builders may like them, but most homeowners will have their eyes glaze over if you bring this up. The goal is to sell homes, not HVAC systems. A home is supposed to be comfortable. Many new ones are not. This link goes into depth on this issue. http://www.healthyheating.com/Thermal_Comfort_Working_Copy/comfort.htm#.Uj9kLr7D_5o

The equation of importance is capital cost to operating cost. Those are best approached with some modeling. I recently completed a model for a 3K sf home with R-25 ICF V 2×4 16OC construction. The operating costs were in the $1,500 range for our utility rates. The HERS Score was 54.

Substituting a GSHP brought the operating costs down by $200 per year and increase the capital costs by 10K. ??The customer opted for the ASHP and ICF over the GSHP and typical construction. He chose where to put his money.

I see a trap in logic using percentages. I provided new construction pricing around here. My cousin in California deals with homes on the bottom range in the neighborhood of 500,000. That makes a hugh difference in the % equation. ??So try rephrasing the question to get some more accurate results. Leave out the percentages.

You have an Energy Star New Home – How accurate are the Projections?

This study is of interest to all HVAC, Insulation Contractors. It is also important to Home Owners.  An Energy Audit makes recommendations and projects cost effectiveness based on a computer model of the Energy Use in each specific home.

How much can you count on those projections? Home Energy Usage depends on three things!

  • First:  The Weather!
  • Second: The Lifestyle of the Family in the Home!
  • Third: The construction of the Home!

Mother Nature has control of the weather! Lifestyle is the difference between having 3 High School Football Players in the family, or 3 High School Cheerleaders.  Energy use will be different. Then what happens to the use when those kids go off to college.

This study actually compares the projections from several hundreds of thousands of homes to their actual usage.  You can read the RESNET Summary. You can read the report itself. I have reprinted the Summary with the link to the Report below.

The original Summary can be read here.

My conclusions:

  • The correlation from projected usage to measured usage over time justifies the reliance on computer modeling using the software to guide your decisions on prioritizing improvements in energy efficiency to your existing home.
  • The correlation of projections for Energy Star New Homes to actual usage gives Builders, Contractors and Home Buyers the confidence to use an Energy Star New Home Certification for lowering the ongoing Operating Costs for Energy in a New Home Purchase.

John Nicholas

 

PROJECTIONS FROM HERS ACCURATE August 22nd, 2012

Posted by RESNET under RESNET News

Over the years, there have been discussions over how accurate are home energy ratings in predicting the energy use of rated homes. To enhance the discussion of the accuracy of home energy ratings’ energy use projections it would be good to review a study conducted and published by Advanced Energy on a large set of homes in Houston, Texas. The authors of the study were Michael Blasnik of M. Blasnik & Associates and Shaun Hassel and Benjamin Hannas of Advanced Energy. The objective of the U.S. Environmental Protection Agency supported “Houston Energy Efficiency Study” was to assess the actual energy use of groups of homes built to different energy efficiency specifications in Metropolitan Houston – typical non-program (baseline) homes, ENERGY STAR® homes labeled by a Home Energy Rating and guaranteed performance homes.

More than 226,000 homes built from 2002 through 2007 by dozens of different production builders were included in this study. The large dataset also provided the opportunity to analyze how certain construction characteristics are related to actual energy usage. Data collected for this project included billing data for all new homes built in the CenterPoint utility service territory from 2002 through 2007, information from property assessor databases of four counties, detailed building characteristics for tens of thousands of ENERGY STAR homes from CenterPoint’s ENERGY STAR Homes tracking database, and detailed data files from energy raters including the home energy rating software tool, REM/Rate, input files and building shell and duct leakage test data. The study did not involve any direct data collection in the field but instead relied upon existing data sources.

This approach allowed the scope of the study to be much larger in terms of the number of homes analyzed but left some gaps in our understanding of some details, especially of baseline homes. The overall dataset includes hundreds of variables for 226,873 homes, including 114,035 potential baseline homes, 106,197 ENERGY STAR homes and 6,641 guaranteed performance homes.

Although consumption differences across groups of homes are smaller than advertised, ENERGY STAR homes perform very close to the predictions of the models on average, while baseline homes perform better than the reference homes defined by the HERS standard. ENERGY STAR uses a base case reference home defined as minimum local code specifications combined with the least efficient cooling, heating and hot water systems available, a leaky building envelope and a poor duct system. Using this yardstick to measure the performance of the ENERGY STAR houses in the study, they did quite well – showing a strong and fairly consistent relationship between actual and projected performance for both heating and cooling. Therefore the apparent lack of savings is attributable not to underperformance by the ENERGY STAR homes but to the fact that the baseline houses in Houston perform considerably better than the ENERGY STAR reference house.

The relationship between REM/Rate cooling load projections and actual electric usage was examined graphically and statistically for 10,258 homes with sufficient data. REM/Rate projected an average cooling load of 5,506 kWh/yr while the billing analysis estimated average cooling loads at 5,677 kWh/yr, about 3 percent higher – excellent overall agreement. Although the analysis found no systematic bias in the REM/rate cooling projections, there was a large amount of variability in the data. Findings revealed that the correlation was higher between house size and cooling load than between REM/Rate projected cooling load and actual usage. However, the study team feels confident in stating that when using current modeling software with energy-efficient new homes, there is a strong and fairly consistent relationship between actual and projected performance using REM/Rate for both heating and cooling. REM/Rate also estimated the average heating usage of program homes fairly well – only 4 percent lower than the measured loads.

To download the study click on Houston Energy Efficiency Study

Ductless Mini Split Heating and Cooling – Is it any good?

I’ve had the concept of a Ductless Mini Split HVAC unit brought up recently. I’m out doing a home energy audit, I’ve been asked on Twitter and in other contexts several times.  A discussion on a Professional Linked In group and my follow up comment has resulted in this post.

First – What is a Ductless Mini-Split?  The simple answer is ‘One type of residential HVAC equipment’.  Other common types of residential equipment are Single Package Unit and a Split Package System. An example of a Mini Split on the right by LG Electronics USA Commercial Air Conditioning. The top image is what you see inside. The bottom two views are of the outside unit. LG is one of many mini-split manufacturers.

If you are building to Energy Star, your HVAC contractor must perform various calculations to figure the size of the units, set up the duct work and select the unit. These calculations are specified by the Air Conditioning Contractors of America (ACCA) an industry trade group. Known as Manuals J (size) D (ducts) N (equipment selection).

If the process and calculations, especially Manual N will show a Ductless Mini Split as fitting the need, great! An example of a Single Package Unit on the right. Outside both summer and winter.

If you are not building the Energy Star – the 2012 recommended Energy Code requires the same process.

If your jurisdiction has not adopted the 2009 or 2012 Energy Code, the prior Residential Mechanical Codes require ACCA calculations or similar. The outside condenser of a Split System on the Left.

Heating and Cooling equipment is routinely oversized in existing homes and in new construction. This approach avoids the math and fits the American image of ‘bigger is better’. It also avoids after hours service calls concerned with the home not heating up or cooling down fast enough.

HVAC equipment, just like your car, operate most efficiently traveling at a constant speed. For your car a highway speed without starting or stopping in city traffic is the efficient speed. Note the Fuel Economy Numbers show the best and the worst MPG figures for each model. At the right is an example of the inside unit of a split system.

Due to the variations in climate from South, with little heating and lots of AC; to the North with a lot of heating and no AC; ACCA uses a design temperature in the calculations. Essentially you can figure the design temperature for your area. The National Weather Service publishes the daily highs, lows and average temperatures for each weather station. The report you want is monthly and is referred to as a J6.

How to figure that is a little much for this post.

A properly designed HVAC unit, like your car will run constantly at or in excess of the design temperature. So these hot summer days, most of us are above the design summer temperature; your AC is OK if it runs all the time. Preventive Maintenance is needed for the HVAC equipment, not sleep.

All that aside; a ductless mini-split is a great choice for a smaller space. My experience with specifying these for Homeowners is that HVAC manufacturers and contractors dearly love them. They are priced accordingly. At the left, the outside duct of a Single Package Unit, typically with no insulation.

 

The Mini Split gets away from the use of ductwork to distribute the conditioned air. That is the strength. Most ductwork in our homes is not designed correctly, it leaks and requires too much fan capacity to distribute the conditioned air. In the right sized space, going without ducts has many advantages.

Thinking About Adding a Solar Panel to your Home?

Last weekend, I spent some time at the Wichita Area Builders Association Home Show at Century II.  I had been invited by Nick King of King’s Solar Wind Plumbing to help out and answer questions about Home Energy Audits.  I got to visit with a lot of interesting people coming through the Home Show. I also got to listen to Nick, Mark, Lee, Tom, Nelson, and Ellsworth about Solar Power for residential and other uses.

I went in with a lot of questions and got the answers.  For this post I decided to take what I learned and put it in a Q/A format for the readers of the blog.  So pull up a chair and read through the questions and the answers.  Then think about the potential of adding solar on your home or business.

Q: What type of energy do Solar Panels provide?

A:  Some panels use the heat from the sun to warm air. This can be circulated into the house; it can be stored in a thermal mass.  This would be a Solar Thermal type panel.

Some panels use the heat from the sun to heat water. The water can provide hydronic (water based) heat or hot water or both. This would also be a Solar Thermal type panel.

Some panels use the heat from the sun to generate electricity. This would be a photovoltaic  (PV) solar panel.

Q: How long does a Solar Panel last?

A:  Many existing solar panels were installed 30 years ago or more. These panels provided hot water or hot air.  Many are still in use and are expected to continue with minimal maintenance for years to come. There are no moving parts on a solar panel.

Q: There are Hail Storms in Kansas!  What happens to my expensive solar system when it gets hit by hail.

A: The solar panels are made of tempered glass. They are rated and tested for a one inch hail stone.  A couple of years ago, a commercial solar array in Texas was hit with a hail storm and stones the size of tennis balls.  A total of 600 panels on this system had only 2 panels damaged.

Q: How do you take care of the batteries, so you don’t have to pay the electric utility?

A: Actually, you want to stay hooked up the to electric utility so you can use them for your battery.  That means no replacements, maintenance expense or other cost.  Kansas Law now requires a 1:1 exchange. When you generate more than you use, the two-way meter, sends it out to your electric utility to deliver to someone else. When you need one, it trades one back.  The planning key is to know what time period your utility uses. Some run the trades for a month and then each month starts with a clean slate.  Some Utility Companies use a different length period, which could be as long one year. Other states may have very different requirements, so check first!

Q: Would my home be worth considering solar?

A: It depends on the solar conditions on your property.  A house with a small yard is best set up for solar by having a south sloping roof.  The sun lower in the winter, a south slope on the roof, helps maximize your solar generation. The other solar condition to consider is shade.  Some parts of your roof may be shaded by parts of your house or by nearby trees.

Q: Do you put one big solar panel or a lot of little ones on the roof?

A:  Most residential PV panels are 39×65 inches.  A typical installation may be 10 to 30+ panels. The actual number depends on your utility usage and your goals.

Q:  How do you figure out how many panels to put on a house?

A: How much electricity do you use? Then how much of the existing electricity that you have been paying for, can you eliminate through efficiency improvements? In this way, you can buy a smaller more efficient system.

Q:  What type of improvements that are energy efficient do you recommend?

A:  Efficient Energy Star appliances are a good place to start. You can look at your refrigerator, deep freeze, the garage refrigerator, and others.  You can look at your vampire loads and look at ways to drop these ineffective or wasteful uses.  The larger savings may be in having your home ready for solar by installing enough insulation or sealing up all the air leaks, and choosing the HVAC system that best matches your needs to efficiency.

Q:  What is the best way to make these determinations about the existing efficiencies of my home?

A:  We recommend a comprehensive Home Energy Audit!  It should include a Blower Door Test with an Infrared Camera testing for air infiltration.  Your auditor should computer model the energy usage on your home as it stands now, and demonstrate the savings of various improvements.

This video from the Department of Energy describes a good Home Energy Audit.

Q: How do I find a good energy auditor?

A: You can check with your Electric Utility Company. You can check with the Kansas Energy Office. You can also check in Kansas and nationally for an auditor with RESNET. If you don’t live in Kansas you can check with your state’s Energy Office.

Q:  I am renting right now and will start building a new home in about 6 months.  How do I make sure my new home is ready for solar?

A:  To start with you should begin planning your home to meet Energy Star Standards.   This would require an Independent Third Party to first review the plans for the home and then to inspect at various times during construction to verify the plans are being followed. As of January 2012, no city, county or other code enforcement authority, in Kansas, has adopted any Energy Code.  If they do in the future, a code requirement for energy would be a minimum requirement, and many of the better builders prefer to build a house that is better than the code minimums.

You can exceed Energy Star Standards to build a new home by having your contractor meet the requirements of the Department of Energy’s ‘Builder’s Challenge Program’!

Q: What if my roof is not the best candidate to mount solar panels on the roof?

A:  You can do a ground mounted system.  It depends on having ground around your home that is not shaded from trees or buildings. You can also calculate the amount of reduction in Solar Efficiency the shading causes, then you can determine if you wish to go ahead.

Q: How many volts does each panel generate?

A: Solar panels are becoming standardized by most manufacturers. A 39×65 inch panel, usually will provide 235 watts of power. You buy electricity from your Electric Utility by the Kilowatt Hour. That is 1000 watts over 1 hour. That means that 5 panels will generate about 1 Kilowatt Hour of electricity each hour the sun shines at peak value.

Q: Why do you say about?  Isn’t it exact?

A: The electricity generated by the solar panel is direct current.  It must be changed, with an inverter, to alternating current to match the electric set up in your home.  The efficiency of the inverter can vary by manufacturer.  The efficiency can be as low as 75% or as efficient as 92%.  I use a 92% efficient inverter.

Q:  Why do you say peak value?

A:  The solar panel generates the maximum power when everything works together.  At 9:30 the sun shines on the panel more directly then when it first started shining on the panel and thus the panel generates more electricity.

Peak Value or Power is also affected by clouds and shade from trees or buildings.  Ten years after you install your solar panels, the neighbor’s trees will grow and perhaps are casting a shadow on your panel. This will change over time.

Q: If a tree is shading my panel part of the day, how much would that really help in the winter after the leaves are gone?

A: The branches would average about 50% of the summer shade value in the winter. The exact amount would depend on the type of tree, how far away it is, and how large it is.

Q;  What is ‘Net Zero’ ?

A:  ‘Net Zero’ is a term that shows your home takes no energy from the utility grid over a period of time, usually a year.  It allows you to trade KWH back and forth, with the end result of no net purchases.

‘Net Zero’ does not mean you are not hooked up to the grid.  That would be termed ‘Off Grid’.

Planning for your home to be ‘Off Grid’ or to become ‘Net Zero’ is the same process with quite different approaches, efficiency parameters, costs and results.  ‘Off Grid is an approach that would appeal to a much smaller number of families than ‘Net Zero’. ‘Net Zero’ is much more affordable at this time than ‘Off Grid’!

Q: Do you have to have an All Electric home to achieve a “Net Zero” status?

A:  No, you can calculate how much extra electricity that your panels produce over your electric needs to offset the natural gas or propane used.

In Kansas, you only get credit for the number of KWH that you trade in and then take back out. Generating more KWH and sending to the grid is a nice thing; but to do this your array is more expensive and thus you have a ‘green payoff’ instead of a ‘cash payoff’!

 Q: Where are solar panels made?  Overseas, like everything else?

A:  You can buy Solar Panels made overseas.  You can also buy panels made in New Mexico or California. Those made here in the US are of the same quality as the imports and the same of better cost.  Also, the energy used to transport them to your home is much less, because they are closer to start with.

Q:  What do I get from adding Solar to my home?

A:  Take your pick!  Save Money!  Go Green! Cut the carbon footprint? It is the right thing to do!

What you get is up to you. You may choose to add Solar for one of these or another reason. The value is for you to appreciate.

For an additional view on Solar, here is a Blog post from Martin Holladay, blogging as ‘The Energy Nerd’.

Common Approaches to Heating Your Home: Part III

This is Part III of a 3 part Series.  Part 1 is here; Part 2 is here.

Hybrid Heat Pump

This choice is sometimes referred to as a Dual Fuel Heat Pump. It utilized both gas and electricity to heat your home. The efficiency of a heat pump is because at most heating temperatures, it moves heat from outside to inside.

Think about your refrigerator. When the inside warms up to 40•, the food risks going bad, so the fridge finds the heat and pumps in out.  Your food stays refrigerated. At 40• outside, a heat pump can find heat and efficiently bring it inside. This costs less than consuming natural gas, propane or electricity to produce heat in a furnace.

At much lower temperatures, a heat pump will need a boost to maintain the heat. This is an electric resistance strip heater. It is used in emergency and back up situations.

A hybrid heat pump uses a conventional furnace for emergency and back up. This is less expensive than electric resistance heat.

Your Choice

In our climate zone; I believe the rank of these approaches should be:

  1. Geothermal
  2. Hybrid Heat Pump
  3. Traditional Furnace / AC
  4. Air Source Heat Pump

This ranking is based primarily on Efficiency Issues with overall comfort issues second.  This rank considers only long term operating costs. It does not consider capital costs (installation).

There are two primary considerations for all of the installation and ultimately comfort issues.

  • The home must be ready for an efficient heating/ac equipment installation.  This means the thermal envelope must be sealed and well insulated. Your thermal envelope is defined as the basement walls, or crawl space walls, the wall above ground, the ceiling.
  • The calculations for equipment size, and selection must be done professionally. The use of a recognized computer program authorized by the ACCA (Air Conditioning Contractors of America); showing the Manual J calculations of the improved home for determining heat loads; and the Manual S calculations to select the equipment. You may wish to have your ductwork reviewed and perhaps resized.  This would call for calculations with ACCA Manual D.

The choice to go with Geothermal or ASHP would mean very little gas usage, only the hot water heater. That could be converted to electric with the ASHP. With a Geothermal Unit, you could utilize a system of hot water that is known as ‘de-superheating’.  It uses otherwise wasted heat from the Heat Pump unit to heat water.

The capital costs of these units in the Wichita area are estimated at:

  • Geothermal:               15-25,000 (open or closed loop)
  • ASHP:                           7 -10,000
  • Hybrid Heat Pump:    7 – 10,000
  • Furnace/AC                 7 -10,000

The Geothermal unit is considered to be a renewable energy source and carries a 30% tax credit, with no limit.  It is available through 2016.

Comfort Note: Conventional Furnaces blow heated air into the duct work at temperatures from 105 – 150; depending and the design factors of the furnace.  If you have come in from the cold and stood neat the supply register of a forced air furnace, you feel the heat.  A heat pump type of heating does not create heat to be blown into the duct work at these high temperatures, a heat pump typically blows air into the ducts at 85 – 105 degrees.  This change can cause people to not like a heat pump; air source or ground source. A hybrid heat pump would provide the same range as a furnace with lower outside temperatures.

Please post your questions below as comments!