Heat Pumps

Heat Pumps: Why Are They Not Being Installed Everywhere?

Every energy-aware citizen immediately falls in love with the technology of heat pumps. They are an incredibly efficient and technically elegant solution to heating and cooling. Then why are they not being installed everywhere? Why would not every residential and commercial building have a heat pump?

In this article I will discuss some of the hidden issues surrounding heat pump technology. Much of the news is good. But there are some caveats that every homeowner should know about before they take the plunge into the world of heat exchange.

First, let’s review the elegance of the technology. Heat pumps move heat.. they do not create heat from combustion. If you’ve opened a fridge door then you’ve used a form of heat pump (fridges move heat from inside the fridge to the coils on the outside). Where does the heat come from with a ground source heat pump? The sun of course. Your property is constantly being baked by the sun. Rain filters through to the water table. Water flows through porous rock. This creates a constant year-round temperature of around 10 degrees Celcius once you dig down 50 feet or so. Now, imagine you put a closed pop bottle filled with 1 degree Celcius water into a 50 foot hole and then haul it back up after a couple of minutes. The pop bottle water will be around 10 degrees Celcius. Now fill the pop bottle with 20 degrees Celcius water and repeat the experiment. The retrieved bottle will also be at 10 degrees Celcius. Heat is being transferred either to the pop bottle or away from the pop bottle. Not a bad little heat pump.

Now replace the pop bottle with a series of closed pipes that push water at a rate of 5 gallons per minute down to depths of 200 feet and back again. Here is where the elegance comes in. The circulating pumps and pipes are completely filled with water+antifreeze solution (all air is bled out) and designed to tumble the water through the piping to get maximum transfer of heat between the surrounding earth and the pipe fluid. Around the pipe is a 4 inch layer of grout (usually bentonite) that ensures good contact with ground rock. By having no air in the pipes, the amount of energy needed to push the water through the pipes is minimized… in effect the water is tumbling through a siphon.

Image courtesy of Natural Resources Canada

And what about efficiency? Heat pumps are rated in Co-efficient of Performance (COP) and will have one value for heating mode and another for cooling. The rating of heat pumps is a good topic for a separate article… for the purposes of this article, all we need to know is that heat pumps can typically move 4 units of heat energy to and from the earth for every 1 unit of energy given as input. Compare this to a typical combustible furnace where 1 unit of energy (e.g. natural gas) produces about 0.8 units of usable heat energy.

Ok.. you are now convinced if you weren’t already.

So why isn’t everyone installing them? Politics? Environmental concerns? Cost?

I will not deal with any political issues. Yes, in most towns and counties you need a building permit and inspections when you install any form of heat pump. But the same goes for combustible furnace installation. I would argue that local and state/federal governments are promoting heat pumps like never before, with rebates that can add up to one third of the total cost.

Then what is stopping the hoped for explosion of installations?

My experience tells me that the main reasons are consumer fear and perceived high cost of ownership. Less prevalent reasons are the inability of the heat pump industry to truly prove environmental safety and the inconsistency of regulation and incentive programs.

Consumer fear is fueled by the fact that almost everyone knows someone who had a bad experience with a heat pump. Do any of these stories sound familiar? Home owner gets a huge electric bill because the heat pump thermostat was not set properly for cold winter nights and the auxiliary electric heat coils kicked in too early and too long. Home owner can never get the temperature just right in their home… the heat pump seems to run all the time and some rooms get too warm while others are too cool. Home owner gets taken in by repair company because home owner does not know the value of any repairs, parts or other maintenance items.

The good news is that most areas now are regulated. In Canada there is the CSA-448 specification that defines the correct installation of both the piping and heat pump. And there is now installer certification through groups like the Canadian GeoExchange™ Coalition. The technology is improving to the point where the heat pump companies (there are some excellent ones in North America) provide guidelines and product for both the thermostat control and the ducting connections for a water to air heat exchange. The old fears should no longer be a concern.

The perceived high cost of ownership is still valid but it is changing. With the rebates in place, the break-even period for a typical family residence is around 8 to 10 years or so if compared to natural gas or oil. After 8 years then the cost of heating/cooling is at least half the old cost (natural gas+electric). Add in the ability of the heat pump to supplement your hot water tank heating and you save even more. You will still require a service contract… heat pumps have a longer duty cycle than regular furnaces (they run more often) so you will need to ensure that they are tuned every year. Once again, the technology in circulating pumps and compressors has been greatly improved over the last number of years. And warranties exist to protect your investment.

So are there really no barriers to adoption? Is it really just fear of past experiences and imperceptions of pricing?

I would love to answer this question with a resounding yes but I cannot. There really are some valid concerns about both the environment and regulation.

First the environmental concerns.

There are many types of heat pump. In the United States, the air-source heat pump is common (which is effectively an air conditioner that can run in reverse). Air source heat pumps don’t work so well in Canada where the air temperature can reach minus 20.

The second common type is open loop water source heat pump. This is where instead of a network of closed pipes, you are pumping well water up to the surface, exchanging heat with it and then pumping the water back down again. Is this bad for the environment? If you search the literature you will find many different opinions. My belief is that it is unknown how dangerous this really is. You are not changing the temperature of the water very much in the heat exchange (only a few degrees) so there is no recorded problem with increasing bacterial growth or other temperature effects. And you are not adding or removing anything from the water, just the heat transfer. But think about how much water is moving. Typical open loop systems move around 12 gallons per minute. Does all this water make it back down to the exact aquifer that it came from? You can’t put it back in the same well (due to both regulation and the physics… you need to move it a fair distance away so that the efficiency is preserved). Now imagine that everyone on your street is moving 12 gallons a minute at the same time.  Problems? We don’t really know yet.

What about our closed loop example we discussed earlier? These move an enclosed water+antifreeze mixture around the pipes and do not draw from any well source. Refrigerant needs to be added to the water in high enough concentration to prevent freezing but low enough concentration to ensure good heat transfer and least amount of pipe friction (pure water is one of the best fluids for heat capacity and fluidity). But what if the pipes break?  Even though the pipes are made from high-density polyethylene (HDPE) it is possible. Then the ground is exposed to the antifreeze. In Canada, most antifreeze used is a form of glycol… designed to be benign in case of breakage. So are there any environmental concerns with closed loop? The biggest one in my opinion is the amount of electricity needed to run the compressors and circulating pumps. Even the most efficient equipment is power hungry, and remember that the heat pump needs to run much more often than regular furnaces because the heat being pushed through the house is lower than traditional furnace output.

So having a heat pump is equivalent to having your electric stove turned on most of the time.  Thank goodness that cheap electricity is still abundent.  But electricity is not clean… at least not in Ontario yet where only 26% is from renewable energy (more than one third still comes from coal, gas and oil generation).  Are my reduced greenhouse gas emissions from eliminating my old furnace being replaced by higher electricity use?

As you can see, the problems are complex. Each homeowner will fumble through this maze of questions on his own.  Myself, I have spent hours making spreadsheets and running energy analysis programs to see where my focus should be.  But I have yet to reach a slam dunk decision.

There are some breakthroughs coming in the future though. New home construction is adopting heat pump technology with water to water exchange (this involves pipes in your flooring where the warm water flows through and radiates the room). These solutions are more efficient than water to air exchange that is usually installed as a retrofit in a house with regular duct systems.

There is a new technology called Direct eXchange (DX) that is coming on fast. It is a closed loop solution without the need for multiple heat exchangers and circulating pumps… the heat pump refrigerant flows through copper pipes and directly exchanges heat with the ground. But currently those systems are quite new and it is unclear how environmentally sound they really are (Will the copper pipe corrode? What happens if it breaks?) Subsequently, in Canada the DX systems are not covered by rebate yet. I have great hopes for DX though because of the greatly reduced electricity needs for operation. My fingers are crossed.

In conclusion, I believe we are at an exciting time in the heat pump industry. Manufacturers realize that consumers want a sustainable solution that takes in to account the electricity used by the equipment. And with rebates, heat pumps (especially in Canada) are not just for the wealthy anymore.

I am anxiously awaiting the changes in technology and regulation that will come in the next few years.

Randy Martin

Randy Martin is a high-tech professional involved in many areas of green energy. He is a graduate of the Canadian Geo-Exchange program (CSA448 Heat Pump Installer) as well as a member of Ottawa Clean Tech (www.ottawagreentech.com), a group of engineers who recommend solutions to residents and business.