Last week I posted a graph of the Cottage daily electric use. This graph is updated every day. While the graph is very useful, it does not include any propane used. While there are many days that the cottage does not use propane, I do expect to use propane for heat this winter. And there were some days in November when propane was used to heat the cottage.
As I suggested earlier, propane and electric use can be included on a single graph of daily energy cost. Electric energy costs me $0.30/kWh in Maine and propane costs $4.29/gal. (I should point out that propane cost would be significantly lower if I used much more propane. My local supplier is currently charging $3.30 per gallon delivered for customers with 1000 gal annual use. So far my use is at the 100-200 gal/year level.)
This month (December) I am using propane heat much more in order to actually compare my propane flow numbers with the amount of propane that is delivered. I received a propane delivery about a week ago, so my goal is to use a significant amount of propane in the next few weeks so that I can use the next propane delivery to calibrate my propane flow meter.
I have performed a preliminary calibration of the propane flow meter — and that calibration is being used to produce the propane costs in the above graph. But I do expect to adjust these figures once I receive the next propane delivery.
Recall from my earlier post that, under conditions that my heat pump had a heating COP = 3.3, propane heat cost was about 2.2X the cost of heat from my heat pumps. So it is with great reluctance that I turn off the heat pumps and heat with propane. Such is the cost of scientific experiments.
A few weeks ago I noticed that the Mitsubishi mini-split heat pumps in my house were consuming considerably more electric energy than those in my guest cottage. This applied especially to the large heat pump (15 kBtu/h) in my house living room which carries the most load.
Since then I have looked at this more closely and concluded that the excessive energy use is assocated with the fan speed settings on the heat pumps. The fans on both house heat pumps were set to Auto while the ones in the cottage were set to High (setting 4 of 5 possible manual fan speed settings). When I switched the fan mode of the house heat pumps from Auto to High their energy consumption decreased by 30-50%. That is, they supplied more heat while using less electric energy. The change was substantial.
The data that support this conclusion are convincing. The first measurements I made were to determine the heating COP for the living room heat pump. I did this 3-4 times on different days with different outside temperatures. I obtained COP numbers like 1.95, 1.15, and 1.14. This concerned me so I reached out to my installer, Dave’s Appliance. They, in turn, told me they passed my information along to Mitsubishi. In the intervening two weeks I have not heard back from either.
I don’t know why but at some point I wondered if the fan setting might be involved. Both guest cottage and house were to be unoccupied for a few days so I set the heat pumps in both to maintain an interior temperature of 60oF, 24-hours-a-day. In addition I wrote a Home Assistant automation to change the fan speed setting at midnight so that I could observe the impact of this change on energy use. I performed this experiment with the 15 kBtu/h house living room heat pump and also with the 18 kBtu/h cottage heat pump. For both heat pumps I observed similar results. The heat pumps used 40-50% less power when the fan mode was set to High as compared to when the mode was set to Auto. I also determined that the heat pump used excess power when the fan mode was set to Medium (3rd of five manual settings). I did not try any of the slower fan settings. I have confirmed similar energy savings when the fan is set to Very High (5th of five manual settings). I believe that these conclusions apply to all four of my heat pumps, though the level of savings may vary.
After I changed the living room heat pump fan speed setting to High I again measured its heating COP. This time I obtained a value of 3.7 when the outside temperature was 30oF.
I should mention that each of my four heat pumps make use of the wireless remote temperature sensor sold by Mitsubishi. It can be purchased on Amazon. In principle, this should seemlessly integrate with my heat pumps.
This seems to me to be an important result. If I were not metering (and paying attention to) my heat pump energy I would not know they are not operating efficiently. They are producing heat and the room is comfortable. Heat pump energy use is not monitored for most installations.
But energy (and associated cost and carbon) savings is the only reason to invest in heat pumps rather than inexpensive electric baseboard heaters. After all, electric base board heaters provide more stable and quieter heat and are cheaper to install. If heat pump operation does not deliver the promised savings the heating costs and carbon footprint will not meet expectations. It is quite possible that thousands of heat pump installations in New England alone are using 50% more energy than necessary because their fans are set to Auto mode. It seems to me that Mitsubishi should care.
I don’t know if this problem is related to my use of remote wireless temperature sensors, or if it also would apply even using the internal temperature sensors. (I will not be able to disconnect my remote sensors in order to test this until I return to Maine after Christmas.) It is possible that Mitsubishi software that controls the fan may be written only for the internal tempearture sensors and is not approriate when connected to a wireless temperature sensor. I have seen nothing on the Mitsubishi web site that suggests this.
I should point out that when one uses either Kumo Cloud or the remote control to change settings on the heat pumps this often changes many other heat pump parameters. For instance, if you point the remote at the heat pump and raise the temperature, the remote also sends other parameters it has saved for fan speeds, direction, etc. Someone might set the heat pump fan speed to High using the Kumo Cloud phone app, then later adjust the set temperature with the remote and inadvertently change the fan (and other) settings to those saved on the remote.
One final comment. I did find that the temperature fluctuations were smaller when the fan was in Auto mode than when the fan was set to High or Very High. So there does seem to be a tradeoff between energy savings and temperature control. Experiments continue to better quantify this.
One of my students, Griffin O’Neal-Freeman, figured out how we can export data from Home Assistant to a Google Docs. This provides a useful gateway for posting our Home Assistant data on the web. Below is a graph showing the daily electric use of the Guest House for the month of December. The graph should be updated daily.
The same graph for November is shown below.
This graph only includes electric energy — it does not include propane. The main reason is that we have to figure out the best way to graph propane and electric energy on the same scale. One possible method is to use Btu — but should this be site energy or source energy? I am leaning towards making a graph where energy cost is the common metric. The propane presently costs me $4.29/gal while the electric is close to $0.30/kWh. (This is an average cost as the cost formula is complicated, beginning with a large monthly fee for just having a connection.)
In the last week or so the energy used by the Rheem HW heater has increased. That is because I switched it from heat pump mode to resistive electric heat. In response to recent rains and elevated outside temperature I ran the dehumidifier in the crawl space. This will not normally be running when the outside temperature is below 40F.
Nate Adams asked whether the heat pump was modulating its electric use to maintain temperature or cycling on and off? The power data (below) show it is cycling on and off.
The graphs below are for the last 30 hours or so and overlap with some of the data I posted yesterday. They also include another night of heating with the 18 kBtu/h heat pump. The first graph is what Home Assistant gets from the Mitsubishi Kumo Cloud interface regarding the settings of the heat pump. The second graph is the Govee temperature data and the third is electric power from both the heat pump (blue) and the electric heaters (purple).
For most of this time I am heating with the heat pump. In early afternoon (2-4PM) solar gain through the windows causes the Govee temperature to rise above set point and the heat pump throttles back. The HP was turned off from 4-8AM yesterday to heat for 2 hours with electric then 2 hours with propane. The electric heater power data are shown in purple.
The first graph clearly shows that the set point (purple) is 63F while the measured temperature of the wireless sensor (blue) bounces between 64 and 65. I simply do not understand why the Mitsubishi control software maintains an average temperature above the set point.
As I have indicated, this heating season I will be using my guest house in Maine to study the energy performance of two Mitsubishi mini-split heat pumps. Already some interesting results are emerging. So far this season, with outside temperatures 23°F and above, the heat pumps demonstrate considerable energy (and cost) savings as compared with electric, baseboard heat. My students and I are starting to quantify the savings. Here I report on some preliminary results.
We have three ways to heat the guest house: 1) Two Mitsubishi mini-split heat pumps (one 6kBtu/h and the other 18kBtu/h), 2) A 20,000 Btu/h Rinnai propane vented wall furnace, and 3) three 1.5 kW ceramic electric heaters (together, 15,400 Btu/h) distributed throughout the open space. Each of these three systems has its own remote thermostat. The heat pumps each have a wireless remote thermostat mounted on the wall across the room. The Rinnai is controlled remotely by an Emerson Sensi thermostat, also wall-mounted across the room. And the three ceramic electric heaters are individually plugged into smart outlets that are controlled by Home Assistant using software to mimic a simple on/off thermostat, with temperature measured by a Govee WiFi thermometer sitting on a cabinet near the Sensi thermostat. Because the Govee thermometer reads in 0.1°F increments, it is the common metric used for determining the Cottage inside temperature.
My Home Assistant Heating Dashboard is shown below. All of the heating and monitoring systems can be remotely accessed.
Solar gain is a big factor during the day, so our heating experiments are conducted at night. Last night we heated the guest house for several hours using three of the four heating systems (just used one heat pump). The results are shown below. The first graph shows the Govee temperature from 4 PM yesterday through 10 AM this morning (11/14). Until 4 AM space temperature was maintained by the 18 kBtu/h heat pump. Early yesterday the set point for the heat pump was 65°F but was lowered to 63°F around 6:40 PM yesterday. At 4 AM the heat pump was turned off and the interior temperature was maintained for the next two hours with the three 1.5 kW electric heaters. At 6 AM heat switched from electric to propane. Both the propane and electric heat had set temperatures of 64°F. At 8 AM the propane heat was terminated and control was given back to the 18 kBtu/h heat pump.
The outside temperature, measured with our Ambient weather station is graphed below. The purple lines indicate when the heating system was changed. From midnight on the outside temperature stayed within 2°F of an average value of about 31°F.
The electric power to the heat pump and the electric heaters were continuously monitored. The average electric power to the heat pump between midnight and 4 AM was 553 Watts. From 4AM to 6AM the electric heaters had an average power of 1830 Watts. That is, the electric heaters used 3.3X the power used by the heat pump. Without adjusting for the change in outside temperature this implies a heating COP = 3.3. This is great news. It means 3.3X lower heating cost than with electric resistive baseboard heat.
But there seems to be a small price to pay for this energy savings. The temperature regulation with the heat pump is not nearly as good as with either of the other two heating systems. The heat pump caused temperature swings of about 2°F while the other two systems have swings of only 1/5th this amount. Moreover, the average temperature maintained by the heat pump is well above its 63°F set point. (Even when you graph the temperature determined by the heat pump’s remote wireless sensor you see that it is always above the set point.) One has to wonder why the control software for the heat pump is not able to do a better job of maintaining the desired temperature. There appears to be no ability to change the “deadband.” for this unit.
We are still working on metering the propane flow in order to understand the energy use for the propane heater. We hope to have this metered soon, it has proven more difficult than we imagined.
But even without metering the propane, I know how much propane should have been burned from 6 – 8AM. From 4-6 AM the electric heaters provided 1.830kW x 2 h = 3.7 kWh of heat. I am paying $0.30/kWh for electric so my cost for this electric is $1.10. 3.7 kWh of energy is equivalent to 12,500 Btu. My propane furnace is rated at 80% efficiency. So to deliver this amount of heat requires that it burn 15,600 Btu of propane. The energy content of a gallon of propane is 91,452 Btu. So I would have had to burn 0.171 gal of propane which, at a cost of $4.29 per gallon, would cost me $0.73.
Hence, 2 hours of heat last night cost me $1.10 using electric heat, $0.73 using propane, and $110/3.3 = $0.33 using the electric heat pump, this with an outside temperature of nearly freezing. The only downside of the heat pump is the lack of temperature control. I am optimistic, however, that we can learn how to use the heat pump better to achieve better control.
One final thing to note is that when I look at the specs for this Mitsubishi compressor, MUZ-FS18N it appears to me that for a wet-bulb outside temperature of about 30°F and a dry-bulb inside temperature of 65°F the heating COP should be 3.21, consistent with my measurement of 3.3.
This post is another follow-up on my earlier post regarding excessive energy use by one of my Mitsubishi heat pumps.
Several times in the past I have reached out to Dana Fischer, Director Regulatory Strategy for Mitsubishi Electric, U.S. He has been very helpful in helping me understand the performance of my Mitsubishi mini-splits. Here is what he had to say about the changes between the older model FH compressor and the newer FS series.
“It is true that a jumper was incorporated into the FS series to allow activation of the compressor heater function where desired but by default reduce oil temperature maintenance to lower energy consumption during standby. Ironically, there are contractors who clip the jumper and turn this function on during installation of FS systems to prevent any risk of compressors having a cold start up if the occupant turns off the system for an extended period during extreme cold then cranks the heat pump on and up while the oil is very viscous. $15 is pretty cheap insurance on a compressor if consumer usage might be intermittent during extreme winter.”
Dana went on to say that that “…. the risk [incompressor damage] is low otherwise the change in default from FH to FS would not have been allowed. Durability and reliability take precedent. I don’t have the jumper clipped on my (2) FS12 units that provide me with all my heat or lose any sleep.”
Meanwhile, I ran my data by Marc Rosenbaum, and he indicated that he has the same issue with his ducted Fujitsu heat pump. He says he eliminates this excess energy by shutting off the breaker to his heat pump during the summer, since he never uses air-conditioning.
All, in all, I am very happy with my Mitsubishi mini-split units. Now that I understand the origin of the power spikes in my one unit I can live with the extra $15 per year of electric use.
A few weeks ago in my post I described how one of my four Mitsubishi mini-split heat pumps was using excessive energy. Today’s post provides additional information about that. Apparently the excessive energy is by design! For background please revisit my August 12 post.
Just a quick recap — In the last three years I have had four, low-temperature, mini-split heat pumps installed on my property in Maine. The oldest of these is a 15 kBtu/h unit that is installed in my house living room. The model number for its outdoor unit is MUZ-FH15NA. The other three units were installed over the next two years. Their outdoor units have model numbers: MUZ-FS06NA, MUZ-FS18NA, and MUZ-FS06NA. (Apparently the “FS” models are improved over the “FH” models.) All four compressors use R410A refrigerant.
These units have seen minimal use since the beginning of May. On rare occasions we have used them for a bit of cooling or heating. They have simply remained in standby mode for nearly 120 days. Three of these use 3-4 W of continuous standby power but the oldest, the 15 kBtu/h unit, particularly during the night, experiences 70W power spikes every two hours or so that last for about 10 minutes. This causes this unit to use about 0.2 kWh per day more energy than the other three. For three months I have been seeking to understand what is going on.
Back in June I emailed my installer, Dave’s Appliance, questions about this performance including graphs and other details. I have always found Dave’s to be extremely helpful. They could not explain what was going on so they passed the information along to their Mitsubishi support team. A couple of months went by with no answer.
I pestered them some more. Finally, in mid-August, two technicians from Dave’s drove the 50 miles from Winthrop to my house to make measurements on the compressor while on the phone with their Portland Mitsubishi tech support. With the travel time, these guys spent a half day addressing my issue. The only measurements they made were to confirm that a certain thermistor had the correct value.
One of the techs who came to my house was Ean Laflin, the heat pump service manager with Dave’s Appliance. After he was done troubleshooting and speaking with Mitsubishi he explained that there was a 70 W heater in the compressor, and that the control board turned it on whenever the ambient temperature was below 68F. Presumably after the heater ran for 10 minutes the temperature of the thermistor rose above the set point causing the heater to turn off. (It is my impression that there is oil in this compressor, and this heater is intended to keep the viscosity of this oil low so the compressor will start easily when called upon.)
But this begs the question, why would this heater be activated when the ambient temperature ranges from 60F to 68F? I could see the need to heat the oil during the winter. But in my part of Maine from May – October the ambient temperature is usually above 68F for much of the day and usually drops below 68F late at night. For nearly four months I have not needed this heat pump yet the heater keeps using energy, night after night. The only way I can avoid this is to shut off the circuit breaker. This is obsurd!
So why doesn’t this same thing happen with my other three heat pumps? Ean tells me that the control board on these slightly newer models is shipped with a jumper that can be set so as to disable this feature — apparently this is the default setting. He can change the jumpers on the other three heat pumps so that all four of my heat pumps run this heater and waste energy. But there is no jumper to change on my Living Room heat pump to reduce its standby power to 3W like the other three heat pumps.
I conclude from this that Mitsubishi, after shipping thousands or perhaps millions of heat pumps with this control strategy determined it was not necessary and “improved” the next generation of control boards. The only way to “improve” my heat pump would be to install a new control board. I recognize this is not a cost effective way to save the $15/year wasted by this heater.
Which leads me to my last point. Each one of my four heat pumps is connected to the internet and can be controlled using the Kumo Cloud App. Why can’t Mitsubishi download updated firmware over the internet to fix this bug? Hundreds of millions of devices (phones, etc.) that only cost a few hundred dollars can receive updated firmware over the internet. Why can’t Mitsubishi figure this out for heat pumps that cost many thousands of dollars? The technology really needs to be updated.
In my Maine Guest Cottage I have installed a 50 gallon, Rheem hybrid heat pump hot water heater. I purchased this unit at Home Depot about 16 months ago. The price was roughly $1600 with a large $800 rebate from Efficiency Maine. My cost then was only about $800. My other option was an electric hot water heater which would have cost me about $600 and did not come with a rebate.
There were cheaper heat pump hot water heaters available at the time but I was enamored by the WiFi interface that came with the Rheem unit. This, along with the Rheem Econet smart phone App, would allow me to remotely change the unit’s settings and also monitor its daily (even hourly) electric use.
The energy guide for this unit suggested that it would cost $104 per year to operate, based on an estimated annual electric us of 866 kWh and an electric price of $0.12/kWh. Here in Maine I pay about $0.30 per kWh for electricity.
I installed the Rheem unit in my unheated cottage crawl space. Most of our hot water use will be in the summer when we actually have guests staying there. Heat pump operation during that period should help dehumidify the crawl space. In the winter months when we do not use much hot water I will likely have to switch the unit to resistive electric mode as the crawl space will be cold and any heat removed from the crawl space air would have to be made up by some other heating system.
This coming winter I intend to make detailed measurements to understand the energy performance of this unit. But already some information has emerged.
The first issue is the inaccuracy of the energy use reported by the Rheem Econet App. For my first six months of operation this was my only measure of energy use for the hot water heater. According to the App the unit was averaging 2.0 kWh/day. For most of this time no one was living in the cottage so that hot water use was minimal. This daily energy corresponds to an annual use of 730 kWh per year — using essentially no hot water use! (That is, this is the energy loss from the 50 gallon tank.) Imagine what the energy use would be if a family of four was using hot water for showers, laundry, and such. I suspected the energy consumption data were inaccurate.
So, I connected up a single-phase iammeter energy monitor to this 220VAC circuit to measure energy use of the Rheem unit. I found that the Rheem unit used significantly less energy than its app reported. The graph below compares the daily electric use as measured by the Rheem Econet App to that independently measured with my iammeter energy monitor for a three month period.
The Rheem Econnet App for this three month period reports an average energy use of 1.88 kWh/day while the iammeter measured 0.62 kWh/day. The Rheem’s own measurements while highly inaccurate, are correlated to the actual energy use. The graph below demonstrates this correlation. The R-square for this fit is 88%.
I do not understand why Rheem has not provided accurate power measurement on their $1600 hot water heater when numerous companies are selling smart plugs with accurate power measurement for $10.
The second problem I have with the Rheem App is that it seems to have a mind of its own. There were times this last year when I wanted to compare the energy use in electric resistive heat mode to that used in heat pump mode. Accordingly I would use the App to set the mode to resistive heat. A few days later, without warning, I would discover that the unit had returned to heat pump mode though I had not made this change. This is something I will investigate further this coming year.
The third problem I found was that the temperature of the water provided appears to be significantly lower than that displayed on the app or on the unit’s LCD display.
Before our first guests arrived this summer I thought I should make sure we had adequate hot water. The Rheem water temperature was set to 120F and it was in heat pump mode. I took a shower. With the shower mixing valve set to maximum hot the shower was comfortable for me. Admittedly, I like hot showers. This caused me to worry that the hot water would not be sufficient for 2-3 consecutive showers. Accordingly I raised the Rheem set temperature to 130F. But I began to doubt that the water leaving the Rheem tank was at the specified temperature.
So I decided to install a temperature sensor in the hot water supply line from the Rheem hot water tank. This was accomplished with a DS18B20 sensor inserted into a 3/4 in. “T” fitting that I installed on the output water line from the hot water heater. I programmed an ESPHome D1mini board to monitor this sensor and connected it to my Home Assistant system. Initial measurements suggest the actual temperature of the water is 10-15F lower than the 130F set temperature.
The last thing I will mention is the instrumentation that we have added in preparation for our full year of study coming up. In addition to the aforementioned temperature sensor, I have installed two water meters with pulse output, one on the water supply line to the guest cottage and the other on the HW supply line leaving the Rheem HW heater. These meters will allow me to monitor CW and HW use in 1 gallon increments.
The other feature that I installed was a “dump line” from the hot water heater. To study the performance of the hot water heater I will need to regularly use hot water. But no one is living in the cottage through the winter. To address this issue I installed a motorized valve downstream from the HW meter that will allow me to remotely, and under program control, “dump” hot water down the drain. This will, of course, result in wasted energy — but this will be necessary to study the performance of the Rheem under conditions that replicate 2-4 people living in the cottage.
In the last three years I have had four Mitsubishi low-temperature mini-split heat pumps installed in Maine. Two of these are smaller, 6 kBtu/h units, one is an 18 kBtu/h unit, and the oldest of these is a 15 kBtu/h unit, located in my living room.
I have been monitoring the electric use of the two cottage heat pumps for more than a year. In March 2023 I began monitoring the energy use for the two older heat pumps in the house.
This post looks at the standby power of the four units. One of the units displays, what I would characterize as strange behavior. I have reached out both to Mitsubishi and to Dave’s Appliance who installed my units and no one has explained the behavior. Perhaps someone reading this post will be able to shed light on this.
These days all four of my heat pumps have power but are turned OFF so that they provide neither cooling nor heating. They are essentially in stand-by mode. As mentioned, three of these heat pumps use about 4W of standby power. A graph of P(t) for the last day or so for my 18 kBtu/h unit in the cottage is shown below.
In contrast to the 4W standby power of the above heat pump, the 15 kBtu/h heat pump in my house living room displays the behavior shown below.
The above heat pump has standby power of about 5W during the day, then starting at midnight, has periodic spikes of close to 70W. These bursts last for only about 10-12 minutes, then re-appear about 2 house later. These bursts stop sometime the next morning, then the pattern repeats the following night.
The excessive energy use is not much on a day-to-day basis. My three heat pumps use about 0.11 kWh per day per unit in standby mode. The one with bursts of power uses about 0.23 kWh per day in standby mode. The excessive use is about 44 kWh per year which, at $0.30/kWh, costs about $13 per year. Again, the excessive energy is not that much — but what is its origin? What is it about the control of this heat pump that is different from the other three?
These graphs just illustrate that a lot is going on in these heat pumps that you would not notice if you don’t measure their power use. They all seem to be operating normally, otherwise.
I would welcome any input if anyone can explain the behavior.
For reference, the model numbers for the 15 kBtu/h units that show anomalous behavior are MUZ-FH15NA for the outdoor unit and MSZ–FH15NA for the indoor unit.
All of the heat pumps are 220VAC units. I monitor their electric use with iammeter single-phase units. The data from these units are regularly logged with Home Assistant.
The town of Oberlin, OH was essentially built on a swamp. Oberlin basements commonly experience water problems. When we first purchased our Oberlin home in 1988 there were a few storm events that left water puddles in our basement. Various measures eliminated this problem, but high summer humidity remains an issue. For years we have employed a basement dehumidifier to prevent mold and mildew.
Our house in Maine also has humidity issues. We are on the Atlantic coast where the relative humidity is always above 70%. Both our house and guest cottage are built on granite ledge sloping down to the water. I wouldn’t have thought so, but it turns out the granite ledge is relatively porous to water flow. After every rain storm, water flowing down the hill towards the river creates water issues in our crawl spaces. Dehumidifiers have proved to be important to prevent condensation on our water pipes and mildew on the wood.
I have read that you need to keep the relative humidity level in your crawl space below 60% to prevent problems. The usual way to accomplish this is to 1) prevent water from entering the crawl space using water and vapor barriers, and 2) use a dehumidifier to remove what water does enter.
I have three dehumidifiers located in 1) our guest cottage crawl space, 2) house basement/crawl space, and 3) our Oberlin house basement. All three are plugged into smart plugs that record their energy use. The two Maine units are commercial units from AlorAirand the Oberlin one is a Honeywell residential unit.
In Oberlin I have a heated basement, so the dehumidifier never has to remove water from cold air. The Honeywell unit can handle that. I do not run it during the winter. In contrast, the Maine crawl spaces are not heated and get quite cold. The AlorAir commercial dehumidifiers can remove water even when the air temperature is in the 40’s. I ran both of them last winter — not sure if I need to and will try to figure that out.
The graph below shows they day-to-day energy use of our guest cottage. As the graph shows, the dehumidifier uses 4-5 kWh of energy daily.
The AlorAir unit uses 600 W when the compressor is running. I normally leave its set point at 60% relative humidity and the compressor cycles on and off. A typical graph of its power vs time is shown below.
When I lower the set point the duty cycle increases (i.e., time that the compressor is on is longer) and the daily energy increases — all as expected.
I am a bit worried about the frequent cycling of the above dehumidifier. I don’t understand why the control doesn’t include a larger “deadband” so that the compressor does not switch on and off so frequently. I attempted to reach out to AlorAir to learn more but I found their technical support to be unresponsive.
The first graph above shows that the dehumidifier used much more energy on July 17. The reason for this is that I decided to try cooling the guest cottage air by circulating it through the crawl space. This exposed a continuous source of humid, warm air to the dehumidifier and it ran nearly continuously. After one day I concluded this was not the optimum way to cool the cottage.
The average energy used by the dehumidifier in my Maine house for July has been 3.4 kWh/day. The area of the house crawl space is larger than that of the cottage, but it is better sealed. Unlike the cottage the crawl space floor in the house is fully sealed with concrete.
The average energy used by the dehumidifier in in Oberlin for July is about 12 kWh per day. Our house there is over 100 years old and all the walls lack modern vapor barriers. The graph below shows the power used by this dehumidifier. This unit removes about 60 pints of water daily and runs almost all the time during the summer.
This dehumidifier is about a year old. My experience with these “basement units” is that they work well for a few years. After a few years they continue to use lots of energy but don’t remove much water. When I bought this Honeywell unit last fall, the dehumidifier it replaced was 4 years old. I ran the two of them side by side for a few days and found the new unit removed water at a rate 5X that of the old one (even though they had the similar specs and were using similar energy). It is hard to throw the old one away because it still removes water — just not good at it.
What I don’t know is the importance of keeping the relative humidity of my Maine crawl spaces low in the winter. My instinct is to believe that mildew and mold won’t grow during the winter in my cold crawl spaces even if the relative humidity is high. But when the temperature warms in the spring I need to keep the humidity level below 60%. But this is just a hypothesis. So far I am erring on the side of caution and running the dehumidifiers year round. They just use less energy in the winter.
I would like to reduce the energy and carbon emission associated with dehumidification. That would be accomplished by raising the relative humidity set point on the dehumidifier. But under no circumstances can I tolerate mold or mildew. I would be interested in learning what people have to say about this issue for cold and warm weather. Is RH% a relevant metric when the air temperature is low as is the case in the winter? Does it make sense to use lots of energy to achieve 60% relative humidity in a crawl space whose temperature is below 45F? I don’t know the answer to these questions and would value informed input.
The Pragmatic Steward 