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New to Heat Pumps

Peacenes · 2021-10-10T09:42:34Z

Hi I exchanged a few emails with Mars and he referred me to this site, and encouraged me to paste my questions and first experience with my newly installed air to water heat pump. I sincerely apologize for this being so long, because I want you all to get a good picture so that you can give me the right answers, and I basically copy-paste my conversation with Mars with a few changes to text Also sorry for my grammar and style of writing, 'cause English is not my native language. I live in Bosnia in the countryside in a double decker house around 230m² (160m² is living area, 70m² is not being used). My previous heating system was a furnace runned on wood and coal. A month ago I installed a heat pump system, with all new piping and larger radiators (Vaillant) specialized for heat pumps. Since the beginning of October I started using it, because we had a really great September till the end with temps up to 26 'C. It's been working a couple of days now with outside temperatures between 2 to 10 'C. Today we have 4 with chilly winds, and the first snowfall in the mountains, Bosnia is mostly mountains, like Switzerland but without the banks :) I had a lot of questions and didn't understand what was the best setup for the heat pump, how to use it efficiently etc. and I didn't quite get the answers from the serviceman, so I googled around (a loooooot) and your videos with your really complex setup helped me the most. Here are some specifics: - 16kW M-thermal Split air-to-water heat pump by MIDEA - it's only used for heating (vaillant radiators) - It's NOT being used for sanitary/domestic hot water (very important) - but I do have a 200l buffer tank, to accumulate hot water (I understand the benefits of that) - house is very good insulated Now I'll explain the setup and how it is working and performing these days and how I think it should work, based on watching your (Mars) videos and reading the manual (because there are many types of setup). So because it's a split system, the indoor unit is located in a room of the house or as Mars called it "nerve center" in his vids, in this room besides the indoor unit is the buffer tank, the main piping goes from there to the radiators, the wired controller which is connected to the indoor unit,my main switches and the external circulating water pump (the usual red one - I'll refer to this one as external, because the heat pump like all has its own internal circulating pump, which the serviceman told me is only powerful enough to push the water to the buffer). HOW IT WORKS NOW So, on the indoor unit the only step I do is to put the unit ON, and set the target water temperature, which is these days on 43'C (I plan to set it to 45, or maybe higher because we have colder winters then the UK), all my rooms get warm enough. The compressor starts, water gets heated up, the internal water pump pushes the water to the buffer tank, I can see the temperature rising on the buffer temp readers. Now before I continue, I have to say that I have a SALUS wireless room thermostat like the one Mars been talking about, but the thing is the serviceman connected the counter part of the Salus room thermostat (the signal receiver) directly and only to the red external circulating water pump. This is what confuses me the most, I asked them why, why not connect it to the heat pump as I read in the manual that it can be done this way and on the indoor unit I can see the connections and writing "for room thermostat" - and they gave me the answer that it is "better" this way and more efficient, i was like OK you are the professionals. Moving on, after turning on the heat pump and setting water temperature (on the wired heat pump interface), I also at the same time set my salus wireless room thermostat to my desired room temp, like 22'C the receiver gets the signal and turns on the red external circulating water pump. From a cold start (water temp. around 18'C), the radiators get to the desired water temperature in about 1-2 hours, if I for example turn the heat pump off overnight and start it in the morning, the buffer tank still has mildly warm water in it around 30'C) so the radiators get warm pretty soon in about 15-20 minutes, so that is a huge advantage of the buffer temp, the heat pump doesn't' have to do much effort like from a cold start. Now we are getting to the interesting part. After reaching the desired room temp on my Salus, it emits to its counterpart to shut off the red external water pump, and it does. Now some would think, depending on how cold it is and on the insulation, the temperature on the Salus would drop eventually and the two would communicate again to get the red external pump on again, but this doesn't' happen...my room temperature even rises sometimes up to 1-2 degrees, and yes it gets to worms in our house...also the radiators doesn't get cold or "cooled off", some would say great but for me it's not, first it's to warm, second to lower the room temp I have to...

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Air Source Heat Pumps (ASHPs)

Last Post by Kev M 4 years ago

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Peacenes

(@peacenes)

Active Member Member

Joined: 4 years ago

Posts: 8

Topic starter 17/11/2021 5:44 am

Posted by: @kev-m

Is there a sensitivity setting on your room thermostat will stop it reacting to small variations in room temperature

Morning,

so this wouldn't let me go, I googled some more about the DIP switches on the back...and finally had what feels for me like a major breakthrough. I blame these poor and outdated little manuals that come with the package and can be found on the manufacturer's website for not getting it sooner, terms like TIP, CHP, hysteresis make sense now 🙂

So I found out that this two switches aren't just simply turning one or two settings on the RT on or off, like changing the sensitivity from +/- 0.5 to +/- 0.25, putting them in the correct up or down position enables one of four protocols or algorithms on the RT, which are controlling the RTs behavior.

By default both switches are down, and in this state the "TPI 6 CPH" protocol is active, this protocol has basically nothing to do with the +/- 0.5 or +/- 0.25 sensitivity change.

TPI (Time proportional and integral protocol) is a self-learning algorithm which calculates the furnace run time, it makes measurements a few times per hour (6cph or 9cph) to predict how long it takes for the furnace to achieve the desired room temperature and according to the measurements turns the furnace on or off. This definitely didn't work for me, and caused the ASHP sometimes to cycle every 10-15 minutes.

So by just pushing one switch on the RT in the other direction I enabled the "Hysteresis +/- 0.5" protocol, this is the simplest two-position algorithm meaning if the room temperature is like 21.7C and I set the desired room temperature on the RT to 22.0C, it won't start yet but wait until room temp drops to 21.5C and than start and work till it achieves 22.5C.

I tested this and think this suites me the best, in the ASHP log for the last 6 hours i can see that running times were from around 60 to 80 minutes, with 40 to 60 minutes off time...so no short cycles.

When my RT wasn't correctly wired to the ASHP, I used the schedule method with similar run times.

So after figuring this out, the only question open would be number 2, related to correctly setting and enabling weather temp set/compensation.

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Kev M

(@kev-m)

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Joined: 5 years ago

Posts: 1276

17/11/2021 9:13 am

@peacenes

Mirnes, good progress. You now have a slightly more clever thermostat, which will switch the ASHP on and off less often, running at a constant flow temp. The next step (I think) is to do the same at a weather compensated flow temp and see how that goes.

What I, @batalto and others are trying, is to bypass the thermostats by turning them up high (so that they are always calling for heat) and let the weather compensation control the temperature of the house by varying the flow temp. Currently, doing this, my house has stayed at 21-22C when it's been between 6C and 12C outside. So far so good but I need some colder weather to test it more.

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Peacenes

(@peacenes)

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Joined: 4 years ago

Posts: 8

Topic starter 17/11/2021 9:47 am

Posted by: @kev-m

is to bypass the thermostats by turning them up high (so that they are always calling for heat)

I understand, but wouldn't that mean that the ASHP is always working, because weather compensation just lowers or raises the waterflow temperature, but doesn't actually turn the unit OFF?

I know when the ASHP is always on, that it runs consistently with less effort, smoother and at lower compressor current which reduces energy consumption, but shouldn't it "rest" now and there (wear and tear)?

You guys surely use the ASHP for heating sanitary water as well, maybe this is one reason to keep it always working.

My ASHP is only used for heating the radiators/rooms (not sanitary water), I have a buffer tank which stores the heated water...so when the unit is OFF for let's say an hour and starts again, it takes just 10-15 minutes for the radiators to get warm again and room temperature rises because it's pushing the stored warm water from the buffer tank.

In these first 20 to 30 minutes, the ASHP is working a little harder (more noisy, higher compressor current) but soon reaches target flow temperature and then goes back to running smoother.

My October bill was surprisingly low using mainly the schedule option or manually shutting it down, things the RT will do now instead of me

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Derek M

(@derek-m)

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Joined: 5 years ago

Posts: 4427

17/11/2021 11:17 am

@peacenes

Hi Mirnes,

Your ASHP will still start and stop when on weather compensation, but should operate more efficiently. There are two main factors which affect the efficiency of your ASHP, one is the outside air temperature, which as it gets colder means that your ASHP has to work harder to extract heat energy from the surrounding air, and the other factor is the water flow temperature. The higher the required water flow temperature, the longer and harder your ASHP has to work to achieve the required water temperature. When your ASHP is operating on weather compensation, the required water temperature is set dependent upon the outside air temperature, but in the same way as your thermostat stops your ASHP when the room is up to temperature, the weather compensation will stop your ASHP when the water is up to temperature. During milder weather conditions the required water flow temperature will be lowered, so your ASHP will not have to work so hard and will be more efficient.

Because you have to select a weather compensation curve from those available, it is unlikely that it will perfectly match the requirement for your home, so you will still need to operate your system with the thermostat controlling the indoor temperature. But by setting the water flow temperature automatically using weather compensation, should improve the overall efficiency of your system.

Do you have any reading of Coefficient of Performance (COP) on your controller?

Just like a car engine, your ASHP is designed to operate for many years, and prefers to operate for longer periods, rather than be starting and stopping.

To keep the room at a more constant temperature you could set the hysteresis on your thermostat to +/- 0.25C, which again could slightly improve the efficiency.

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Kev M

(@kev-m)

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17/11/2021 11:48 am

@peacenes,

Mirnes,

Here are a couple of graphs that show my ASHP working your way and then my current way. The first is 24 hrs, the second is 6-7 hours. Take care looking at the y-axes; the scales are different although the units are the same.

Here, the ASHP is responding to a thermostat with the flow temp controlled by weather compensation. It's set to 21C morning and evening and 18C at other times. From midnight, it's coming on periodically because the ambient temp is 5C or below - that's automatic. I assume it's to stop watrer pipes freezing. In the morning and evening the ASHP responds to the thermostat and comes on. In between the house stays at 18C or above so no heat required. The peak midday is hot water. In the evening you can also see the thermostat stop calling for heat, making the ASHP turn off and then calling and starting up again. The energy peaks are high, although the ASHP is off a lot of the time.

Below is with the thermostats turned up. As @derek-m says, the ASHP isn't heating all the time if it doesn't have to. Most of the time it runs for a bit then stops. These cycles are every 30-40 mins. When it gets a bit colder (look at the blue line), it can run at its minimum level constantly.

As Derek also says, these units are built to last for years. They are the same technology as your freezer and fridge and these don't break very often. My freezer compressor turns on and off all the time.

Which way is better? Well currently my house is warm all the time, which is nice. The ASHP is running more efficiently (better COP), which is good. But, it's running for more time. Is it cheaper? I suspect it is, but I don't know yet.

Hope this helps.

This post was modified 4 years ago 4 times by Kev M

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