The Hype About Heat Pumps

Heat Pumps have been used widely for decades but recent developments have made them “cooler” than ever.  Here’s what you should know: a heat pump is, simply put, a device that transfers heat from a colder area to hotter one using mechanical energy, typically using a vapor compression refrigeration cycle.  Refrigerators, air conditioners and freezers are good examples, although the term heat pump (HP) is usually used for systems that heat spaces and possibly air condition.

There are many sources or, “heat sinks,” used to extract and deposit thermal energy.  They can be air, the earth or waterFor example, a geothermal heat pump transfers energy from the earth or water to air, which is then used to distribute the heat inside the conditioned area.  There are numerous types of heat sinks, and associated terminology such as air-to-air, air-to- water, water-to-water, etc.  The simplest and most common is air-to-air which has also been getting the most buzz lately.

When used for heating, HPs can improve comfort and indoor air quality while significantly reducing heating energy costs. Here is a recent chart of comparative heating energy costs.
Energy Comparison Chart

Here is a model of a typical indoor split unit.

Here is a model of a typical indoor ductless split unit.

As you can see, air-to-air HPs can be one of the least expensive ways to heat a space.  Costs rival geothermal, natural gas and even firewood, which begs the question as to why haven’t they been used more in the past.  There are characteristics that challenge their usage.  The performance and efficiency of air-to-air HPs drop as the temperature difference between heat sinks increase.  For example, the capacity and energy use of an air conditioner gets considerably worse on really hot days. Similarly, performance and efficiency drop when using HPs to heat a space on extremely cold days.  The performance of a HP is rated by its coefficient of performance, or COP. This is a ratio of the energy moved divided by the energy required to run the device.  Simple electric heat, for example, has a COP of one.  For every kilowatt purchased it yields one kilowatt of heat energy.  Modern and efficient air-to-air HPs have COPs ranging from approximately 3-4 when used for heating.  Not bad, compared to electric heat, huh?

The challenge is that the heating output or capacity drops during the coldest outdoor temperatures precisely coincident with the times increased capacity is needed.  Historically, air-to-air heat pumps were sized less than the maximum heating capacity needed since they would be grossly oversized for cooling (air conditioning) use in the summer months.  This especially the case in northern climates where the winter has colder outdoor temperatures. The use of HPs in more southerly States has been more widespread because of the milder winter design temperatures. The “capacity droop” challenge historically required the use of supplemental or backup heat sources such as fossil fuels, or most commonly electric heat. These sources made the economics of HP heating much less attractive.

So what changed? The reliability, availability and use of variable frequency drives (or VFDs).  Nearly all new and modern HPs are variable speed.  This solves a major technological challenge; we can now size the system for the heating load without causing the equipment to short cycle, or rapidly start and stop while cooling, which tears up equipment and prevents good performance for cooling and dehumidification.  During both heating and cooling modes the systems will ramp the speed and performance from anywhere between 10-100 percent.  This enhances performance, equipment longevity and reduces noise.  Dehumidifying performance is greatly improved as the unit runs longer at lower speed, enhancing moisture removal.

HP systems can easily be installed during new construction, but until recently they were more challenging as retrofits.  Air-to-air systems distribute thermal energy via airflow. Many, if not most homes in the northeast have hydronic heating systems, thus no existing ductwork.  Achieving a good outcome retrofitting ductwork can be expensive, invasive and challenging.  In the heating mode, the typical warm supply air temperature is 80-110 degrees F, thus poorly designed airflow can create draftiness and discomfort.  Fortunately, the “ductless” option alleviates this challenge.

Ductless Heat Pump Outdoor Unit

Here is a model of a typical outdoor ductless split unit.

In the early 1980’s, the first imports of ductless split system heat pumps began to arrive from Asian manufacturers. These were popular in countries like Japan, where typical living spaces are quite small by American standards. These ductless systems distribute air indoors directly from wall or ceiling mounted air handlers. They are compact, and very quiet to operate. One manufacturer even sells a unit disguised as a wall mounted fine art painting, where air silently passes in all directions from behind the frame.  American manufacturers fought off the market penetration of this new disruptive technology for almost thirty years mainly by tightening codes, standards and implementing arcane testing criteria. Asian manufactures found ready markets in less developed countries of the Middle East, Caribbean and South America, where their use became commonplace in smaller commercial and residential spaces. Finally, the American market embraced the technology about five years ago, and today utilization has increased substantially.  Several major US producers have purchased manufacturers in Asia and began production in the US as well.

Although these high efficiency air-to-air units come in a variety of systems configurations, the wall mounted indoor unit is most popular. Due to the size of the unit and low powered fans, air filtration is very limited. The ducted version can be supplied with much higher efficacy filtration and can even have central humidification added for the dry winter months.

In commercial applications, both ducted and ductless split system heat pumps are an effective solution for difficult to heat and cool areas due to their installation flexibility. Centralized HVAC systems serving the building might not offer such flexibility.

It is important to note that most split system heat pumps do not satisfy criteria for fresh air required by those versed in “best practice” and building codes. Outside air can be introduced in the ducted versions, but typically require an uncoupled parallel ventilation system such as an air-to-air heat exchanger to adequately introduce fresh air.  Thus, unless additional provisions are made, the ductless split system heat pumps do not satisfy building ventilation needs alone.

At Thayer, we first witnessed testing of the innovative ductless split systems in 1982.  They performed well and could have been very useful to our customers.  The bad news is that we had to wait nearly twenty years for them to be commercially attainable and UL certified in the US.  The good news is that now they are available, competitively priced, very reliable and extremely efficient.

In the last year or so, we designed several geothermal heat pump systems but found the high efficiency air-to-air systems have similar performance at a lower installed cost.  An ironic twist to the relative ease of installation is the recent proliferation of installing contractors who do not have HVAC experience, qualifications or expertise.  Maine was lobbied by special interest groups to make exceptions to normal technician licensing and this has resulted in a sharp increase in faulty installations. Although they are relatively easy to install compared to other system types, they still require proper selection, sizing, location and commissioning for a well working system.

In our state, Efficiency Maine has been promoting heat pump use for select high efficiency models with a $500 incentive which helps defray new system cost.

There are no “silver bullets” in the HVAC and energy efficiency marketplace.  No one source of energy is “best.”  We have what we like to call “silver birdshot;” We evaluate each building, and explore all possible options.

If interested, we can have one of our engineers evaluate your needs and develop options. “Call in the Experts” at Thayer.



Dan Thayer, P. E.

President, Thayer Corporation

The Problem with Programmable Thermostats

Ecobee smart control thermostat

The Problem with Programmable Thermostats

Most commercial buildings use some form of time of day control for the heating and cooling systems.  Larger buildings are often equipped with centralized building management systems (BMS); however, the vast majority of buildings that are not large enough to justify these often costly systems must rely upon programmable thermostats.

Programmable Thermostats come with a very wide variety of features, ease-of-use and functionality.  Their price range varies, starting anywhere from $50 for a simple unit to $500 for “fully loaded” models.  Almost all of them are able to accept unique programs for each day of the week.  Some thermostats even allow for extraordinary events such as holidays.

The newest generation of programmable thermostats are called “smart thermostats” and include features such as electric meter communicability, remote access control via a computer or cell phone, and in some cases they may even learn and adapt to occupancy profiles.  Although growing in popularity, smart thermostats represent only a very small fraction of the installed base in commercial buildings.  Many of the more popular ones still have somewhat limited applicability to commercial HVAC systems.

So what’s the problem with programmable thermostats?  It’s basically this: rarely are they properly programmed or fully utilized.  Almost universally, their utilization isn’t optimized. There are a variety of reasons for this, so let’s explore a few.

If you have ever had teenagers living in your house, you know how maddening it can be to find lights illuminating an empty room, doors ajar, computers and televisions left on and even windows open while your heater or air conditioner is running.  This isn’t because they are bad people; it’s just that the month’s utility bill doesn’t come from their allowance.

The same problems usually exist in commercial buildings.  The occupants most directly affected by the HVAC systems don’t see them, and are very rarely the ones to pay the bills.  Those of us who are “comfort professionals” can attest that there are many varying opinions as to what the “right” temperature is.

We certainly all have seen this: an occupant sneaks by the thermostat, cranking the temperature up to where only inhabitants near the equator might find it comfortable.  A few minutes later, another staggers over, and before mass dehydration sets in, drops the temperature to where the windows begin to frost.

This causes building owners and managers to resort to imprison thermostats in silly looking cages, which often exacerbates the frustration that occupants feel over their comfort control. Some occupants become very creative, and find clever ways to trick and open these thermostat covers, or trick the thermostat’s thermometer.  So, at minimum, there is often a conflict between the interests of the occupants, and those who foot the bill.

Let’s examine another major—yet simple—reason why programmable thermostats don’t work well to save energy: the person with the vested interest in the energy costs isn’t the one programming the thermostats.  Well-intentioned owners, managers and maintenance staff usually will input a basic program at the time of installation, but rarely is there someone to regularly review these programs, which is necessary to tweak them to reflect the current schedule and usage of the building.  As the saying goes, “out of sight out of mind.”

Unfortunately, many programmable controls aren’t intuitive to use, let alone program. Documentation gets misplaced, and the previously trained operators forget, get transferred, or simply aren’t available.  Service providers typically don’t have access to the key person who can make decide on the necessary programming parameters of daily, weekly and annual schedules, let alone what the “appropriate” temperature levels are.

When I write my memoirs, there will be at least one large—and very amusing—chapter devoted to the many “thermostat wars;” creative approaches to tricking controls (i.e. car keys, lighters and bags of ice) and occasional outlandish requests for set points or systems performance, “Madam, we sympathize over your hot flashes, but please understand, your air conditioning systems isn’t designed to hold your office at 55 degrees; the industry considers that refrigeration.”

It’s extraordinarily uncomfortable for the service provider and or installer, such as us, to be asked to install a “dummy thermostat.”  Simply, these are thermostats that are placed for the occupants to fiddle with, yet don’t control anything except, often their perceptions.  Thankfully we very rarely get these requests.

Some of the newest smart thermostats are relatively inexpensive and accept basic time-of-day programming, yet will automatically reduce HVAC system operation when there is no activity observed.  We call these occupancy based smart thermostats. They allow the occupant to easily adjust the temperature and override a setback program (i.e. working late or on weekends) while still allowing the building manager to pre-program set point limits to reasonable levels.  They can be networked via innovative wireless networks, have remote accessibility, can be connected to the HVAC unit with wireless connections, track energy utilization and consumption, and even look attractive.

A lack of maintenance, faulty installation and poor designs are often the cause of discomfort within a building.  Thorough and comprehensive maintenance will identify and eliminate many of these maladies, but the newest generations of occupancy-based smart thermostats are useful tools in minimizing wasteful operation and delivering optimal occupant comfort. Most of them compile and display information about current and historical usage enabling owners and occupants to make more informed decisions about system usage. Allegedly it was this type of occupant activity and usage that attracted Google to recently buy Nest for a whopping $3.2 Billion.

Call one of our personal energy conservation and comfort specialists here at Thayer today for an evaluation of your building.  Additionally, send us your favorite picture of an antiquated, “user-modified,” interesting, worst location and/or downright wacky thermostat for a chance to win a free iPad Mini!



Dan Thayer, P. E

President, Thayer Corporation




To Freeze, or Antifreeze?

To Freeze or “Antifreeze”

Burst Frozen Pipes

This winter season has set many records for severity across the entire US and Canada.  One record it’s unlikely you’ll find data on is freeze-ups and frozen pipes within buildings. Anecdotally, there are a record number of these unfortunate disasters this heating season.  Frozen pipes often burst, causing severe building damage and loss of use, and are extraordinarily difficult to thaw.  Not only have we experienced severely cold weather, but the coincident wind has made the “chill factor” of buildings much colder than usual.

Often there are conflicting views on protecting hydronic heating systems with antifreeze. Practitioners such as plumbers and heating technicians are often poorly informed, relying upon wholesalers for information.  Even system designers are frequently misinformed.  The debate is often emotional and illogical, so here are a few facts to help you make a good decision about its use.

The type of antifreeze used in HVAC systems is typically glycol.  Most of the glycol used for these applications has added corrosion inhibitors.  Some benefits of adding inhibited glycol to a system include:

  • Prevention of system freeze-ups and bursting pipes and coils when properly applied.
  • Allows for deeper temperature setbacks without a freeze risk resulting in reduced energy usage.
  • Reduced corrosion within piping, boilers, coils and valves leading to longer life.
  • Reduced scaling in boilers and heat exchangers thus maintaining higher efficiencies.
  • Minimal issues with toxicity (if propylene glycol is used).

All of these benefits presume that the glycol solution is properly maintained annually.

Some of the risks or disadvantages are:

  • Initial cost of adding and maintaining solution.
  • Slightly higher pumping power required.
  • Reduced heat transfer from coils, heat exchangers and boilers.
  • Larger expansion volume necessary.
  • More difficult air elimination from system.
  • System flushing and clean-up might be required on “dirty” systems before the addition of glycol.

Let’s explore these a bit more.  First, it’s necessary to determine which protection level you need.  Some prefer to protect to a very low temperature point by adding more glycol, say to as low as 0-10°F.  It’s also possible to protect the system to “burst point,” which is approximately 30° lower than the freeze point, say -30 to -20°F.  At the freezing point, the solution won’t flow, but the pipes and coils won’t rupture.  Once heat and/or pumping are restored, the “slushy-like” solution melts and becomes fully liquid again.  The higher the concentration of glycol, the higher the first cost and negative impact on heat transfer and pumping power.  Generally, it makes sense to protect to the higher burst temperature criteria.  For example, a 20% solution of propylene glycol by volume would yield a freezing point of 17°F, a burst temperature of approximately -10°F, require 3% more pump power for equivalent flow, and impede heat transfer by 3%.  This alone cannot be the total answer as to system performance.

The glycol used for heat transfer applications is generally propylene glycol (P/G) with corrosion inhibitors.  Ethylene glycol also has good performance characteristics, but due to toxicity concerns, we don’t recommend its use.  P/G is very different from automotive antifreeze, which contains silicates which tends to gel, impeding flow and causing problems especially in flow control valves.  P/G is not toxic and is widely used in many applications such as a solvent and carrier of flavor or color in the food and beverage manufacturing processes, to make drinks, biscuits, cakes, sweets, as a thickener, clarifier and stabilizer in consumables such as beer, salad dressings and baking mixtures.  P/G is also used to keep tobacco semi- moist.  Ever wonder what keeps Twinkies soft for so long?

The maximum working temperature of the P/G solution is 250°F.  For ordinary heating applications, this isn’t at all a problem, but care must be taken on closed-loop solar heating systems.  It is quite possible for the fluid flow to become stagnant in the collector plates if the controls aren’t properly working.  Temperatures can easily reach this upper limit causing the P/G to break down and become acidic.

Occasionally, P/G is added to hydronic systems that provide cooling (i.e. ice arenas). Obviously the working temperature for cooling is much lower than heating which results in a much higher solution viscosity. This more viscous solution is harder to pump and impedes heat transfer more than at higher temperatures. Both of these disadvantages must be planned for.

The corrosion inhibiting properties of glycol reduces scale build up, especially in boilers.  Scaling is quite common and reduces heat transfer significantly; for example, a 1/8” scale build up in a boiler results in 30% more fuel usage overshadowing the minor heat transfer loss from the addition of antifreeze.  As the performance and efficiency of boilers and heat exchangers has steadily increased over the past two decades, the surfaces have become greater and passages smaller making them much more difficult, if not impossible, to clean this scale buildup.

Many of the strong opinions about glycol in HVAC systems from designers, installers and service technicians are a reaction to some of the challenges working with the solution.  A few of the major challenges are:

  • A water/glycol (aqueous/glycol) solution has a lower surface tension than water alone and will leak where water doesn’t.  This is especially true on automatic air bleeding valves, causing “weeping.”
  • Glycol is an “oxygen scavenger,” making air elimination much more difficult during the initial system fill.  It can take several days to bleed all of the air out of a system.
  • Annual maintenance is required to assure that the concentration, pH and general fluid quality are acceptable.  Deficiencies generally can be corrected by adding more glycol, corrosion inhibitors and/or pH correction.  Neglected systems can turn acidic and deteriorate pipes, valves, fittings and equipment.
  • Care must be taken not to isolate sections of piping or equipment such as a valve; the solution needs to be able to expand into the expansion tank upon a system freeze event such as power outage.
  • The expansion tank needs to be slightly larger than a water only system.

Automatic fill valves should be eliminated to prevent inadvertent concentration dilution in case of a small leak.  These lists aren’t intended to be a complete list of do’s and don’ts or design considerations, but hopefully provide more information to help guide your decision.  If interested, consult one of the professionals at Thayer to determine the feasibility for you system.  There’s nothing worse than the expense, damage and the “coulda, shoulda, woulda” that often follows a catastrophe such as a building freeze up.  Act now, and “Call in the Experts.




Dan Thayer, P.E.