Tag Archives: heating and cooling

The Heat Pump debate

space conditioning, ,

The motivation to switch to a heat pump is often rooted in the desire to reduce heating costs. I get that.

High heating costs are typically associated with inefficient buildings that have a poorly insulated and drafty building envelope. Such buildings would need a rather large heat pump with a ducted or multi-zone set up, or even several heat pumps.

Our building with a subpar building envelope prior to any improvements

Anecdotes from heat pump forums, acquaintances, and friends indicate that owners of buildings with a subpar building envelope often regret switching to heat pump – mainly because their electrical bills went through the roof. If building owners assume that heat pumps are a quick fix, their conclusion that heat pumps are a waste of money, and that it is cheaper to heat with natural gas, is on fairly solid ground. But if building owners approach heat pumps as part of a broader systemic plan, heat pumps can and do generate significant cost savings. 

The system approach

We have a masonry building, built in 1902, with three apartments. Each apartment has its own airsource heat pump (single head minisplit), which is placed centrally in each apartment.

They run great! They provide the needed cooling during the summer and just about the right amount of dehumidification. They provide the needed heating during winter, even during spells of subzero temperatures. And they heat significantly more cheaply than our hydronic baseboard radiators that are powered by a high efficiency natural gas boiler.

But why?

The minisplits are only ONE component in our system approach. Preceeding and prerequisite components in our system approach were the improvements to the building envelope during our deep energy retrofit, which allowed us to substantially reduce our overall energy load: Roof insulation; wall insulation; foundation insulation; basement slab insulation; triple glazed, airtight windows; insulated exterior doors with good weather stripping; air sealing; etc. All these efforts reduced the energy load of the building by around 2/3 and catapulted us into cost-effective airsource heat pump territory.

Now that we had reduced our energy load, I could build on it with the next component: “right sizing”. I hired a competent energy auditor to run an energy model for each of the three apartments to determine the heating and cooling load.

Undersizing heat pumps is not a good idea as it will be difficult at times to keep the building warm or cool enough. Oversizing heat pumps introduces its own problems, such as short cycling, which in turn reduces efficiency and comfort, and can lead to insufficient dehumidification during summer.

The results from the energy model allowed us to go shopping for the “right sized” equipment.

We installed a 9,000 Btu cold climate Fujitsu minisplit in the garden unit (900 sf), while the 1st and 2nd floor apartments (1,500 sf each) have a 12,000 Btu cold climate Fujitsu minisplit each.

In addition to the heating and cooling loads, I paid close attention to the moisture removal capacity of the minisplits, to make sure they deliver a comfortable relative humidity level during the dog days of our Midwestern summers.

For us, the next component in our system approach was looking into a renewable energy source. Because our space conditioning load was drastically reduced, reflected in the three relatively small heat pumps, we could power them with our photovoltaic roof array. The result, thanks to our net metering agreement, is next to no heating or cooling cost.

Our electricity cost per household compared to the Illinois average. Our electricity use includes all cooling and most of the winter heating with our minisplit.

Taking a system approach, we were able to turn the paradigm on its head: Our high efficiency natural gas boiler cannot compete cost-wise against our heat pumps.

Disclaimers

But it’s not all unicorns and rainbows.

Heat pump installation requires professional expertise, attention to details, and skills, in particular when it comes to sizing and the flare connections. To avoid a never-ending loop of service calls, it is a good idea to be picky about who you let near your heat pumps.

Yes, the right heat pumps work in freezing temperatures. Our cold climate minisplits even powered us through a brief polar vortex with subzero temperatures. However, the colder it gets, the less efficiently they run. I observed that our heat pumps notably lose efficiency once we drop below 20F. They still do the job. They just draw more power.

Heat pumps are likely to run differently compared to your old heating system. If you had forced air, you turned it on and it was warm 10 minutes later. That is unlikely to happen with heat pumps. They ramp up slowly but efficiently. With heat pumps, you can enjoy more even temperatures, day and night.

Heat pumps can emit an unpleasant stale and moldy smell in the summer (see also this blog post). This happens when they run in cooling or dry mode and are turned off. The remaining condensation on the coil of the indoor unit combined with dust particles is the perfect petri dish to grow mold. This can be avoided by running them in fan mode for a few hours before turning them off. That will dry off the coil. No moisture, no mold.

And like everything else in a house, heat pumps require regular maintenance. You want to make sure to regularly clean the filters and drain lines. Also inspect the outdoor and indoor coils, and the indoor blower wheel, and have them cleaned by a professional when needed.

These are not deal breakers, at least not for us. But it’s good information to have, in case you also want to turn the paradigm on its head.

Related posts:

Minisplit cooling pause

space conditioning,

A typical summer in Chicago comes with heat and humidity that is every now and then interrupted by cooler spells with lower dew points. Those spells can be pleasant enough for us to stop running the minisplit in cooling mode and instead open the windows.

Once the heat and humidity roars back into town, we shut the windows in a hurry and power up the minisplit for that pleasant cool breeze. Except, there isn’t much pleasantness in that breeze, unless you enjoy a musty and mildew-drenched flavor.

If you abruptly stop the minisplit in cooling mode, the fins on the evaporator/condenser will still be drenched in condensate droplets. It is not easy to see in the above pictures, but believe me, the droplets are hiding in there.

And they will be sitting there for several days like a bunched up, wet towel in the corner of someone’s bathroom. If, after a few days, you dare to pick up that towel and give a sniff, you experience a similar flavor to that of the minisplit after it had been paused for a few hours or days. It is a death knell to indoor air quality (IAQ).

The good news is that this is an easy to solve problem. Rather than abruptly stopping the minisplit in cooling mode, switch it to low speed fan mode, and let it run for half a day or overnight. The fan keeps drawing air across the fins and will slowly dry them out.

It’s like taking your wet towel and hanging it up to dry. That towel definitely will smell a lot better – and so will your minisplit once you start it up again in cooling mode.

If you would also like to dry out the condensation collection pan at the bottom of the indoor unit, keep the minisplit in fan mode for a good day. This is definitely recommended at the end of the cooling season (end of summer).

And if you turn off cooling mode for a week or longer before starting it up again, you may want to consider cleaning the condensate drain line, as described in the previous post, just to be on the safe side.

Related posts

Minisplit cooling startup

space conditioning,

Cooling season has started. Our living space has been comfortable in terms of temperature and humidity since we turned off the heating mode on our minisplit back in March. Now it is time to bring the temperature and humidity down a notch so that we can sleep comfortably at night.

The last time the minisplit ran in cooling mode was about eight or nine months ago. Since that time, dust may have accumulated in the condensate collection pan. Once that dust mixes with the first condensate from the heat exchanger coils, it may cake up and block the drain line that is supposed to safely evacuate the water to the outside.

If that is the case, you will notice water droplets on the luvers and a water puddle on the floor under the minisplit.

It’s time to turn the minisplit off and clean that condensate drain line. Or, even better, as a routine maintenance item, preemptively clean the condensate drain line at the beginning of each cooling season.

To do so, find the discharge point of your drain line, which typically would be outside the building. Take a wet/dry shop vacuum with a narrow nozzle. Fit the nozzle over the drain line and proceed to evacuate any water, dust and crud that may have accumulated in the drain line since it last ran in cooling mode. Once the vacuum doesn’t pull any more water or crud out of the drain, start up the minisplit in cooling mode and monitor whether you get any more spillover from the condensate collection plan on the indoor unit. If you do, repeat the cleaning process. If you don’t, great job, and enjoy your cool building interior!

Related posts:

Minisplit winter operation

space conditioning, ,

Our minisplit kept us cool during the dogs days of summer this year, and without having our electrical bill going through the roof.

But the minisplit can do more! Because it’s an air-source heat pump, it also can heat the building during the cold season. And that was something I wanted to put to the test when it recently was really cold outside.

Like I mentioned in the video, I simplified my explanation about how the system works. If you would like to read a more comprehensive and accurate description, you can find it in a previous blog post with the title “Mini what?”

The morning after I took the video, our outdoor temperature had dropped to -5F, the specified minimum operating temperature. I turned the minisplit on and indeed, it still was putting out heat.

While the outdoor unit was almost inaudible during the summer when we ran the minisplit in cooling mode, it was humming away pretty good in the heating mode, as you can hear in the video. I assume that the compressor has to work harder at these cold temperatures, thus the increased noise. Not that it matters. All windows are firmly shut anyway, keeping the noise out.

Related posts:

2016 heating savings

heating, ,

It is friggin cold outside, and I can’t shake the urge to keep talking about heating related matters, so here we go again:

One goal of our deep energy retrofit was to save energy, and along with it, some Benjamin Franklins. The money we invested in tightening and insulating the building was meant to save us dollars on our heating bill, for instance.

But how would we measure how much we save? Our problem was that we had no starting point. We bought our building as a foreclosure in 2009 and thus had no data – no access to utility bills – that would tell us what it took to keep the building heated and comfortable.

That said, there are plenty of buildings in our neighborhood that could serve as a comparable (comp). Not only are they the same construction type, but also in the same energy deficient shape as our building was before we started with our deep energy retrofit.

I found a building that was a good match, and the owner that was happy to share their utility data with us.

To compare apples to apples – or in this case, therms to therms – I calculated the amount of therms used per square foot per month for both buildings. Our building’s natural gas consumption is reflected in the blue bars, while the comp, or pre-retrofit state, is reflected in the red bars.

Data reflections

Why is there natural gas used during the summer months (off heating season)? Because in both cases natural gas is used to produce domestic hot water, i.e. washing the dishes, running the washing machine on warm or hot cycle, taking a shower, etc.

You may have seen me bragging about turning our heat on as late as mid November. If you look at the consumption for November 2016, you see that we mostly used domestic hot water while our neighbor in the comp building had the boiler already buzzing away.

Looking at the big picture, our building consumed 0.200 therms/square foot over the course of one year, while the comp usage was at 0.976. Our deep energy retrofit improvements appear to have reduced our natural gas consumption by 0.776 therms/square foot/year. That equals a reduction in our heating needs from November 2015 through December 2016 by a whopping 80%!

For our metric friends (i.e. the world with the exception of the U.S.): Our natural gas consumption equated 63.04 kWh (or 226.95 MJ) per square meter, while the comp came in at 307.89 kWh (or 1108.39 MJ) per square meter.

I typically don’t like to measure the improvements in cost savings, as supply cost and taxes may vary between jurisdictions or energy companies. In addition, the fixed costs on the gas bill, although often small, prevent accurate scaling to a square foot basis.

Yet getting an approximation of the monetary savings would give us a sense of the potential return on investment. We paid $0.27 for natural gas per square foot over the course of a year. The cost of the comp were $0.98. The estimated total cost savings for the 2,900 square foot of conditioned space in our building from November 2015 through December 2016 would be in the range of $2,000.

Yes – I am beaming right now! Yet, this somehow seems too good to be true. I think the flaw with my analysis is that I have based it on one comp only. I plan to find another couple of buildings that I could include in the analysis. That should give me a number that would be easier to defend.

Stay tuned, because I will keep you posted!

Related posts: