Heritage Restoration, Inc.

Heating Analysis Case Studies

“At the end of the article you stated more or less flat out that the thermostat should be kept at a fixed setting. I agree doing that might be right in some cases. But whenever that is done, it should be understood that doing so increases heating costs. And it does so in 100% of the cases where the thermostat setting is kept constant.- The science here is actually very simple. The rate at which heat is lost from the house goes up as the inside temperature is raised higher and higher above the outside temperature. So lowering the thermostat always reduces the rate at which heat is lost, and thus saves both energy and money.”

 

Jean

 

I did say flat out “keep it at a fixed setting” although the spirit of the article was do your homework.  So I apologize for doing the same thing I was criticizing: there is a one-stop formula for every building.  Jean is correct is saying that you will save energy and money by lowering your thermostat.  Were we differ is that keeping the thermostat at a constant will cost you more money 100% of the time.

 

There are a lot of variables that dictate the ability to maintain and recover heat.  You cannot use strict science to apply to every building.  Here is a recent case study to illustrate the point.

 

Building 1

Conditions

Building 1 is a late18th century granite construction.  It was originally a carriage house, where the stones were laid in some mortar, although there are plenty of gaps.  The interior was stud framed and plastered in the late 19th century.  There is some insulation in the attic.  There is steam heat with a 20-year-old boiler.

 

Assessment

The first thing was a blower door test.  Airflow was a huge problem.  The storm windows were old and drafty (being there does not make them efficient), basement windows were loose and windowpanes were missing, and doors were not weather-stripped.  The steam boiler was not maintained well and the system was functioning poorly.

 

The goal was to make the building more efficient without spending a lot.  The budget was about $15,000.  We replaced the storm windows and repainted the window trim.  The basement windows were reattached or boarded up and sealed (all reversible of course).  The doors were weather-stripped.  The boiler was tuned and cleaned, return pipes replaced and bleeder valves replaced.

 

Since the building is an office with a steam system (which recovers very quickly) they turn the thermostat up and down about 5 degrees.  So far, they are saving about 36% in fuel consumption and about 33% is costs.  About a 12-year pay back.

 

Building Two

Building Two’s zone one is a massive space, about 50 feet by 100 feet with ceilings soaring to 70 feet.  The building is granite with stud walls and plaster for interior walls.  The old oil heating system was steam, and they used the building once a week.  They cranked the heat to 70 on Saturday to Sunday and kept it at 50 the rest of the week.  The steam heat generated a lot of moisture that was causing condensation damage in parts of the building.  They spent close to $18,000 a year in heat.  The system had failed and required replacement.

 

The second zone was forced hot water radiators, which we kept for savings despite them known to be inadequate by the heat calculation.

 

Treatment

We replaced the system with 4 high efficiency forced hot water gas fired boilers that would rotate based on demand.  At first, we had a hard time keeping the temperature by raising and lowering the thermostat, since the building had tremendous heat loss and the mass was so huge.  When we kept the thermostat at more of a constant, the system performed perfectly.  The reasoning was the system was designed to be efficient, with the water staying at the lower temperature of 185 degrees, instead of the old 220, so the system ran better at a constant, even through they needed heat once a week.

 

The second zone was already inadequate, so keeping it at a constant was the only way to make it work.

 

So far, the cost savings are about 43%, with about a 25-year pay back.  A combination of switching to gas and the high efficiency boilers are what is making the savings.  The building is also healthier since it stays at more of a constant heat.

 

This is why science is sometimes trumped by field condition variables.

 

 

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