heat pump -elect coils

[Chris Lewis]

Note that there are some programmable thermostats that "understand" heat pumps. There are some that are smart enough to bring the temperature back up from the set back in increments of a few degrees at a time, so the HP never thinks it's gotten too far behind. There are others that "know" that the abrupt temperature discrepency (between room temperature and setpoint) is due to their "returning from setback", inhibit backup heat, and force the HP do do all the work. The latter have to be built into the HP I believe.

[Chris Lewis]

According to Red Green :

Up north of that border, geothermals (and other forms of ground-source) HPs are becoming quite popular and well known. We had a guy come in to give our house a full workup and provide an quote for switching our house over from baseboard electric to geothermal.

IIRC, he quoted us a 5 ton unit (2200 SF two floor house, _almost_ R2000 construction). This geothermal "style" involves drilling a 100' bore hole per ton (minimum 10' apart), dropping a loop of tubing down each hole, and backfilling.

There were "combination" and "separate" units. The separate units were were the air handler and air heat exchange was one place, and the control box and pumps were in another (close to where the wells are). The "combo" unit is when it's all in one box. The "separate" unit was thought to be more effective for us.

As I recall, the full quote (including $3K for ductwork - we have a very open-concept house, and we were going to be able to "cheat" a bit and still get proper airflow) was around $18K.

In contrast, a straight forced air gas furnace install (not including ductwork) would be $7K - there is no gas in this area, though there may be in another year or two.

The claim was our heating power consumption would decline by about

60%. I worked it out having a break even point of about 10 years. We decided to wait a few more years and check again - they have us on their calender to call back, but they're doing so much business now, we may have to call them ;-)

Do google searches for "geothermal ontario" and you'll find _lots_ of references/descriptions of how it works, installers etc. We get rebates for installing geothermal now. H'm, the break even just got a lot shorter ;-)

[Chris Lewis]

According to BobR :

If the exchanger is horizontal, and only by a few feet (unless you're comparing Miami and Resolute Bay of course ;-).

Many of the systems are vertical (eg: the ones we were looking at use 100' deep wells), so different frost depth makes very little difference.

[Beach Trading Company]

Thanks for that Chris. This unit has the Carrier Infinity Control thermostat. This thermostat know's what components are attached to it and it monitors and controls the system. Their implementation apparently thinks it's more efficient to have the backup heat kick in if the temp needs to be raise beyond a certain number of degrees. I'm told that's 3 degrees. I've decided to only drop the temps overnight a couple degrees and see what the impact is on my electric bill next month. Of course as soon as I did that the temps rose to the 60's and

70's so the HP won't run anyway. ;-)

Rich B

[Paul M. Eldridge]

Hi Chris,

A friend of mine installed a new setback thermostat for his heat pump (a Honeywell as I recall) that monitors how long it takes to return to the daytime set temperature and adjusts the timing of the ramp up period accordingly; in other words, the heat pump comes on earlier during colder weather so that the house reaches the desired temperature at the time requested. He tells me his backup elements never come on as they did previously with his previous thermostat and his operating costs have dropped accordingly.

I always chuckle whenever someone tells me heat pumps don't work in northern climates or when temperatures routinely fall below 40F. Compared to my oil-fired boiler at 82% AFUE, my heat pump has cut my overall heating costs by more than half -- an average cost of just 4.3 cents per kWh of heat versus 10.8 cents for oil.

Cheers, Paul

[Paul M. Eldridge]

Hi Chris,

In addition to the geothermal option, I might recommend looking at one (or more) Fujitsu ductless heat pumps. The operating costs would be slightly higher than a geo-exchange (but not by much) and it wouldn't provide DHW (perhaps its biggest drawback if your household uses a lot of hot water), but the upfront costs would be far lower and the installation a whole lot simpler. Generally speaking, these units are a good choice for energy-efficient, open concept homes such as your own.

The current generation of Fujitsus with the inverter drives work down to -15C (5F), although I'm told by someone who lives in Montreal that his continues to operate all the way to -20C (-4F). I've crunched the IRR and NPV numbers for the Fujitsu based on our local climate and energy costs (7,800 HDD / $0.1067 per kWh) and I know of nothing that matches its technical or financial performance. These truly are in a class of their own.

Cheers, Paul

[Chris Lewis]

According to Beach Trading Company :

What happens is this: most HPs think that a discrepancy of over N degrees (somewhere around 5) means that the HP is unable to keep up, and backup heat is essential to get the heat back to where you want it ASAP. It's not more efficient, it's _quicker_, a simpler programming choice, safer choice (more likely right without more complicated analysis/sensors), and more in keeping with what the designers think _you_ want ("I'm freezing, MORE HEAT NOW (*&&^)(*&!").

It sounds as if you're doing your setbacks manually. If that's the case, the Tstat isn't designed for that, and is going to make suboptimal choices - when you set the Tstat up, it thinks "my owner is cold, I'll warm him up ASAP!". If you want to continue doing that, make your temperature changes gradual. Or use a diferent thermostat.

On our HP/gas backup, we went with a programmable control unit that physically moved the control on the existing thermostat. There were no other options for controlling HPs at the time. I understood about backup issue, and since the unit permitted me to make as many as 20 or so programmed-time temperature changes, I simply set a single "setback" step, and a series of gradually rising "recovery" steps. Worked fine - our heating bills were ridiculously low (for the great white north that is). Just took a while to program.

[Chris Lewis]

According to Paul M. Eldridge :

I think I've heard of these before too, but I forgot.

I get more than a chuckle when people claim to quote supposed professionals who claim HPs are crap. I know which professionals to avoid.

Short of having your own power or heat generation (a gas well on the property would be real nice ;-), a _properly_ chosen and installed HP will beat anything else. Unless electricity prices really jump disproportionally over gas and oil.

Yup. In any climate, an air-source HP plus gas backup will do better than straight gas - even if they only do heating during spring and fall. But geothermal HP will do much better than that, and cares little about outside temperature - BTU output remains approximately constant/same efficiency, it's a matter when the BTU output isn't enough to keep up with heat losses.

We were told that the geothermal unit that was spec'd for us would, on average, rely on backup approximately 30 hours per year - the nights that dip below -40F/-40C. We usually get a week or two where the daytime highs doesn't exceed -25C, and once or twice daytime highs of around -40C. Much like Montana winter temperatures.

[Chris Lewis]

According to Paul M. Eldridge :

It sounds about perfect. Will definately have to look into them. Your friend's Montreal home will be almost the same climate as ours - we're (rural Ottawa area) a little colder, but less snow.

Hey, neat, I can run 'em off the existing baseboard wiring!

Our house is situated amongst heavy tree cover, so, A/C tends not to be necessary more than a few days per year. Because of the way the house is designed, a single 12000 BTU "window type" (actually mounted through the wall) A/C is more than enough. T'would be nice to be rid of the ugly thing - it's at least 17 years old, and it has to die someday. Probably soon.

The trees also aid with heating, because there's less loss due to wind cooling.

I don't think we're particularly heavy DHW users, so, that's not as important. The dishwasher and clotheswasher are both very low water consumption units, and we only do showers.

[Paul M. Eldridge]

Let me pull Environment Canada's hourly temperature data for Ottawa and plug it into my spreadsheet and see how the numbers might work out for you. Without knowing much about your home's heat loss(*) and lifestyle, the results will be necessarily broad brush, but it still might help you determine if a Fujitsu would be a good fit for you (we can refine things a little further after you've had a look at the preliminary findings). I should have something ready for you later this evening.

Best regards, Paul

(*) You mentioned your 2,200 sq. ft. home is near R2000 in terms of its construction, so I'm going to estimate your average heat loss at a little less than 170-watts per degree C, with a demand point of 13C (i.e., when outside temperatures rise above 13C, we'll assume internal gains such as lighting and appliances and passive solar would be sufficient to keep your home at a comfortable temperature). Again, we can make adjustments as you see fit.

[Paul M. Eldridge]

Hi Chris,

As promised, I've built a spreadsheet model using Ottawa's 2007 weather data to estimate the potential energy savings of a Fujitsu

12RLQ ductless heat pump (I'm hoping 2007 is typical of most winters). This particular unit has a nominal rating of 12,000 BTUs/hr cooling and 16,000 BTUs/hr heating, so it's a little undersized for your home and local climate. For our purposes, I've assumed the low temperature cut-off point is, in fact, -15C as stated in the technical documentation and not -20C as I've been told antidotally. I've also assumed your heating season begins October 1st and ends April 30th; if it extends a little beyond these two points, your actual savings would be a slightly greater than what we see here.

If your home's average heat loss is 0.170 kW per degree C and your demand point is 13C, the numbers break down as follows:

Annual Heat Demand 12,738 kWh Heat Pump Output 7,436 kWh Heat Pump Input 2,481 kWh Annual COP 3.00 Net Savings 4,955 kWh Backup Requirement 5,303 kWh Heat Pump Contribution 58.4%

If, in fact, your home's heat loss is a little higher (i.e., 0.20 kW/C) and your demand point is 15C (i.e., the other internal gains previously mentioned are not quite as significant as first thought or if you prefer to keep your home a little warmer), the numbers work out as follows:

Annual Heat Demand 16,913 kWh Heat Pump Output 9,118 kWh Heat Pump Input 3,010 kWh Annual COP 3.03 Net Savings 6,109 kWh Backup Requirement 7,794 kWh Heat Pump Contribution 53.9%

I believe you pay just over $0.101 per kWh, so your dollar savings would be $502.00 and $618.00 respectively ($567.00 and $699.00 including federal and provincial taxes). By comparison, a geo-exchange heat pump with an annual COP of 4 -- if that's a reasonable number to use -- would reduce your annual heating costs by $967.00 and $1,284.00, for an additional savings of $466.00 and $666.00 respectively ($526.00 and $752.00 with PST & GST).

If the geo-exchange system you priced is $14,500.00 after rebate(s) and the Fujitsu ductless unit is $3,500.00, say, after its $400.00 rebate, the $11,000.00 difference between these two options extends your simple payback by an additional 15 to 20 years, or perhaps 10 to

15 years assuming a more rapid escalation in electricity costs. If time permits and if it would be helpful to you, I can work out the NPV numbers to more accurately gage the relative merits of both.

Cheers, Paul

[Paul M. Eldridge]

Hi Chris,

A PDF copy of my preliminary analysis is available at the links listed below:

Fujitsu 12RLQ - Low Demand

Fujitsu 12RLQ - High Demand Fujitsu 15RLQ - Low Demand Fujitsu 15RLQ - High Demand Keep in mind, these numbers are somewhat pessimistic in that supply and demand must be perfectly matched for each hour of every day and if the heat pump cannot supply the entire load in any given hour, the backup baseboard heaters carry the rest. In reality, your home probably has sufficient thermal mass to ride out many of the minor fluctuations in hourly output and thus the need for backup heat wouldn't be quite as great as what we show here.

In addition, we assume a constant temperature must be maintained at all times and you can minimize some of the variations in night time versus daytime performance through temperature set back (i.e., let the temperature in your home drift downward overnight when the relative performance of your heat pump is diminished due to colder night time temperatures). Likewise, if you keep your heat pump set at 21C, say, and your backup baseboard heaters at 18C, you can further enhance your heat pump's overall contribution, especially during the milder times of the year.

I tend to push things a little further in that I often boost daytime temperatures a little higher than normal to take advantage of the heat pump's better performance during the warmest part of the day (during the shoulder seasons in particular, the spread between daytime and night time temperatures can be fairly substantial). I also closely monitor the weather forecast and if temperatures are expected to fall in the coming days, I run my heat pump flat out and bank as much excess heat as possible (within the bounds of comfort); this surplus heat is then used to "ride out" any deficit in production during these colder times. This involves a little extra effort on your part and, again, requires your backup heat to be set a few degrees lower than your heat pump, but the potential energy savings during times when temperatures are bouncing all over the map can be huge.

Hope this information is helpful to you. If you have any questions or if you'd like me to change any of the assumptions used in these scenarios, please let me know.

Best regards, Paul