Using a Nest smart thermostat with an Air Source Heat Pump - What are the optimum settings?

  • 29 November 2021
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J
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Hi there,

I’m having issues with Nest turning my heating on early enough. My heat schedule is 21C during the day, 19C from 9:30pm, then back to 21C at 7:30am. My understanding is that overnight the Nest is supposed to look at the temp change to 21C at 7:30am, look at the current house temp, and the temp outside, and figure out when to turn on such that the house reaches 21C at 7:30am

It never even gets close for me. Usually the house gets to 21C at 9am or later. This morning was the worst so far, I assume because it was so cold overnight (-3C). It turned on at 6:45am, which is insane. It takes about 3 hours on a cold morning to get from 19C to 21C.

 

Right now the temp is 21C. If I use the Nest controller and set the heat to 22C, it says “in 20 mins”, but there is no way the heat pump can change the heat that fast. It would be an hour plus.

In the nest app controls It says “Time to Temp → Ready” and “True Radiant → On Ready”

Anyone else having issues or is it just me?

 

Thanks

James

 

11.2k Ecodan ASHP. 4 Bed semi.

10 replies

nealmurphy
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Hi @James_N 

I have 2nd gen. Nest and it seems to be behaving itself once it’s got its facts together about what it thinks the heat pump is doing. 

I’m wondering if you need to reset the ‘Time-to-Temp’ setting, although in doing this it is likely to start off by not switching on early enough (though if it’s doing that anyway you perhaps don’t have anything to lose). Also, I’m not sure if it makes a difference, but what heating input type is set on your thermostat?

One other thing that may be confusing things: is the heat pump set to weather dependent? If the heat pump is altering the desired flow temp based on the weather it may mean the Nest is trying to second guess the output of the heat pump, although my Nest seems to be putting up with this setting without too many issues.

I’ve upped the overnight temperature from 18 to 19.5 to reduce the effort the heat pump has to put in. The last couple of nights Nest has chosen to go to 21 degrees (the morning temp) at around 2am, though the system didn’t run continuously overnight.

The wall insulation and windows in my house could do with an upgrade hence the heat pump having to work harder and start earlier than it would in an ideal situation.

J
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@nealmurphy Thanks for your reply.

Under system details, heat source is set to “electric” and heat type is “radiator”. - Is that what you mean by heating input type?

Yes, I have a compensation curve running, so that could be confusing it a bit. I think that would make it over shoot rather than undershoot though (?)

I’ll let it run one more night and take a good look at it tomorrow morning, and if its still terrible I will try resetting the time to temp setting.

I think they need to create bespoke heat pump estimations. For example, switching over to heat the HW delays heating the house, but this can be predicted quite easily when no one is using the HW. Also my heat pump today was having to run defrost cycles which also slow down the heating a lot. 

 

11.2k Ecodan ASHP. 4 Bed semi.
J
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Quick update on this. This morning the heating turned on at 7:05. Its supposed to get to 21C by 7:30. It actually got there at midday

I phoned the installers and asked them. They told me not to use the smart settings. Just tell it what time to turn on and off. Which is fine, but totally defeats the point of buying a £150 smart thermostat. 

So I wonder if Nest just isn’t compatible with heatpumps, or if my settings are all wrong

11.2k Ecodan ASHP. 4 Bed semi.
nealmurphy
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I'm slightly tempted to bypass the Nest and see how the heat pump does by itself in cold temperatures. On the basis that the Nest could be calling for heat most of the time I'm guessing the heat pump could do a more efficient job as at least it would know when it was getting close to the desired temperature and start ramping down the output, rather than Nest just switching it on and off whenever it liked.

By the way, I've got my 'heat type' set to geothermal as I though that would represent the slowest heating input and most similar to a heat pump. Though I believe the 3rd gen. Nest has a heat pump option.

J
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Think I may have figured it out. I’ve had the log burner on the last few days. I bet that is messing up its data

11.2k Ecodan ASHP. 4 Bed semi.
Jess_OVO
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Some really great peer-peer support happening hear to help get those Smart thermostats optimised to control your Air Source Heat Pumps (ASHPs) @James_N and @nealmurphy!

 

I suspect this might be an issue that others will face when making the change to an ASHP heating system so I’ve moved this thread over to our public Smart Home area (with your permission!)

 

Anyone else keen to hear about smart thermostat/ASHP compatibility? Comment below and our community members will be on hand to share their first-hand experience!

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Tim_OVO
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@Roy_and_Becky this is the topic I mentioned - you might find what/who you’re looking for here ^

Carbon neutral - we need a community to get there! My green tech: Aclara SGM 1411-B smart meter, Chameleon IHD6
V
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I’m having issues with Nest turning my heating on early enough. My heat schedule is 21C during the day, 19C from 9:30pm, then back to 21C at 7:30am. My understanding is that overnight the Nest is supposed to look at the temp change to 21C at 7:30am, look at the current house temp, and the temp outside, and figure out when to turn on such that the house reaches 21C at 7:30am

It never even gets close for me. Usually the house gets to 21C at 9am or later. This morning was the worst so far nest thermostat not heating at nigh, I assume because it was so cold overnight (-3C). It turned on at 6:45am, which is insane. It takes about 3 hours on a cold morning to get from 19C to 21C.

 

Right now the temp is 21C. If I use the Nest controller and set the heat to 22C, it says “in 20 mins”, but there is no way the heat pump can change the heat that fast. It would be an hour plus.

In the nest app controls It says “Time to Temp → Ready” and “True Radiant → On Ready”

Anyone else having issues or is it just me?

 

hi any chance you could share what your nest schedules look like? I've been battling to get the heating right in my place I believe that 19C is the best temperature now what does your schedule look like?

Tim_OVO
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Let’s see if we can get you some advice on this, @vokar. Although @James_N might need a tag email notification to see this…

 

@simonbkUK is also a known Nest owner...

Carbon neutral - we need a community to get there! My green tech: Aclara SGM 1411-B smart meter, Chameleon IHD6
J
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Hi there,

 

My post is old. I have realised that really a Nest is overkill for a heatpump. Mine is simply set to 20C during the day, and then a set back to 18.5C over night. This works really well for me

 

Nest does look very nice though!

11.2k Ecodan ASHP. 4 Bed semi.

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