MYLOUBYLOU

New to the world of ASHP!

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Hi all, we moved into a 5 bed new build home in August which is a highly insulated timber framed house with an Ecodan 14kw HP and are trying to get to grips with it. Our heating engineer installer is trained but hasn’t had a lot of experience so we are not totally convinced it is set up optimally.

 

There are 2 of us, working from home.

 

We currently have space heating on 6.30am-9pm as we like a quiet house while we sleep. Hot water programmed for 5.30am-6-30am and again 6.30-7.30 at night.  Bedrooms set for 19 degrees, and main living areas/studies are 21. Our en-suite floor temp is 23.  Each room has a heat miser stat and none of them are switched off.


It is a bit of a shock not having hot water all the time but was costing a lot. We switch on the boost before having shower and have nice hot water but during the day we have cold/tepid water to wash hands.  Anything you might do differently here?

 

In this mild weather the rooms come up to temperature pretty quickly. I think we may be seeing short cycling though. Every hour when heating is on but none of the rooms are calling for power, it fires up the HP when the flow temp drops to 38 degrees and then raises it to 55 before letting it drop again.  Looking at the energy monitor it uses 2kwh whilst doing it & not sure what the benefit is to it or us!   If anyone has answer for that that would be great. One thing to know is the connector to call heat isn’t currently installed as we have towel rads that we’re going to be separately heated when space heating isn’t on. Doesn’t seem to get them hot so we are getting this changed. Hopefully this will fix the above behaviour.


The return flow temp is often higher than the flow temp, not sure how that’s possible?

 

Lots to learn!

 

 

 

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A few things spring to mind.

 

HOW is the heat delivered to the rooms by under floor heating, radiators, or a mixture.

 

When ALL the rooms are up to temperature, can you still hear the low level hum of a water circulating pump running somewhere? 

 

You say when HW is off, you only get tepid hot water from the taps.  That does not sound right.  Can you post some pictures of your hot water tank and any other pumps and controls you can see?

 

Assuming you have a hot water tank, once it is up to temperature it should stay there all day only losing a little heat through losses.

 

What is this "boost" that you switch on before a shower, again can you post a picture?

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Hi, and welcome.

You say you are limiting the time the HW cycle is running because it is costing too much. Can you give more detail? How much? how are you identifying that the cost is hot water production? What temp is the HW set to?

 

HW is better left on all day, rather than limiting it to 2 x 1 hour slots. Do you know what temp your HW tank drops to and what the ASHP can lift it back up to in an hour?

 

For your space heating, do you have a buffer tank, or does the ASHP run directly to UFH or Radiators? If the latter, is there a permanently open loop so the ASHP has a min 100l of water to push around? 55°C is high for space heating, is that the temp you have it set to? and where is that measured, flow or return? In a very well insulated timber frame with UFH you'd expect a flow temp of around 35°C

Edited by IanR
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A couple of further questions that will help with understanding the set up...

 

Floor area of the house

Volume of the hot water tank

Do you have MVHR

Do you have PV

 

Are all the pipes fuly lagged?

 

Hot water when on cost alot... how much power was being used?

 

Good luck

 

M

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40 minutes ago, MYLOUBYLOU said:


The return flow temp is often higher than the flow temp, not sure how that’s possible?

 

My guess would be either an electrical element - immersion heater is on somewhere or the hotter hot tank water is flowing back to the ASHP when the heating is on or, if you have a buffer tank, when starting up the hotter water in the buffer tank returns to the cold ASHP, or the warmer water in the heating pipes enters the ASHP when first turned on, or something else, and all explanations give by other more knowledgeable people than myself!

 

The only way to offer up suitable explanations would be to know when it happens, how long it happens, what is operational when it happens and what the temprature differences are.

 

 

M

 

 

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Hi all, thanks for taking time to reply!

 

From EPC floor area is 278 square meters is 89B energy rated.  Walls 0.15 ave thermal transmittance, Roof 0.11 and Floor 0.13. Windows high performance  glazing 

 

Its ufh heating throughout and hot water tank is 300l. It heats up to 48 degrees, save once a week legionella cycle. It drops significantly after a shower, to about 24 but if the boost is used then second shower is definitely warmer than that. 
 

To provide above water uses about 3kwh. 
 

No buffer tank and don’t think immersion is being used other than the legionella cycle. 
 

No PV and no MVHR.

 

We have a weather compensation curve set up, from what I’ve read & if am understanding it correctly it is a bit high -  If it’s 10 outside the flow will be 40 degrees.

 

sorry if missed a question in your responses, will have another read through after work 😊

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The rapid drop in DHW temperature concerns me.  A picture of the HW tank might help.

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10 minutes ago, ProDave said:

The rapid drop in DHW temperature concerns me.  A picture of the HW tank might help.

Me too!  It drops a degree every couple hours otherwise. I assumed it was filling up tank with cold water when the hot was consumed so was mixing. I think the temp probe is midway down tank so figured there is warmer water at the top

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Follow that white cable coming out of the timeguard and tell us or post a picture where it goes to.

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Just now, MYLOUBYLOU said:

Me too!  It drops a degree every couple hours otherwise. I assumed it was filling up tank with cold water when the hot was consumed so was mixing. I think the temp probe is midway down tank so figured there is warmer water at the top

Yes what should happen is hot water leaves the tank at the top and cold water goes in at the bottom.  Little or no mixing happens so the "transition" just moves up the tank.  Even hours later there should still be hot water at the top of the tank to draw.  It is only when the hot / cold transition reaches the temperature probe, which looks to be about half way down, that the HP senses the drop in tank temperature and re heats it.

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25 minutes ago, MYLOUBYLOU said:

hot water tank is 300l. It heats up to 48 degrees, save once a week legionella cycle. It drops significantly after a shower, to about 24 but if the boost is used then second shower is definitely warmer than that. 
 

To provide above water uses about 3kwh. 


To heat 300l of water from 24°C to 48°C requires 8.4kWh of energy.

 

If you're saying you are using 3kWh of electricity, then that sounds about right as with a COP of 2.8, your ASHP will generate that 8.4kWh of energy.

So that doesn't sound like the ASHP is relying on an "additional heat", direct electric element to support the water heating. So heating of the water sounds to be working correctly.

Like @ProDave says, it's the heat loss that appears to be the anomaly. Unless you have a very high flow rate on your shower, and you need the ASHP to come on sooner to start heating the water earlier when the temp drops.
 

25 minutes ago, MYLOUBYLOU said:

No buffer tank


To stop the short cycling on space heating you need enough UFH loop to be permanently open so that the ASHP has around a 100l volume of water to push around. A Buffer would be better.
 

Edited by IanR

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1 minute ago, IanR said:


To heat 300l of water from 24°C to 48°C requires 8.4kWh of energy.

 

If you're saying you are using 3kWh of electricity, then that sounds about right as with a COP of 2.8, your ASHP will generate that 8.4kWh of energy.

So that doesn't sound like the ASHP is relying on an "additional heat" direct electric element to support the water heating. So heating of the water sounds to b working correctly.

Like @ProDave says, it's the heat loss that appears to be the anomaly. Unless you have a very high flow rate on your shower, and you need the ASHP to come on sooner to start heating the water when the temp drops.
 


To stop the short cycling on space heating you need enough UFH loop to be permanently open so that the ASHP has around a 100l volume of water to push around. A Buffer would be better.
 

It’s a rain shower but we don’t spend that long in there. 
 

numpty question but how do I know the ufh loop is open? 

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2 minutes ago, MYLOUBYLOU said:

So does that suggest that only half the tank is up to temp?

Possibly.

 

When the ASHP is heating the tank, the water within it will be circulating by convection and mixing.  It will stop being heated when the temperature probe senses it has reached demand temperature.  Is there a lower thermostat pocket?  I found I got better results (more hot water) by putting the temperature probe in the lowest pocket which is about 1/3 the way up the tank.

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Do you know the flow rate of your shower?

Only needs a jug and a stop watch to check it out.

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I don’t think water is being circulated unless hit the boost on the premise it’ll sit in the pipes cooling which is a waste.  Or will this not happen as much as the slab is up to temperature?  Keen to understand as much as possible before cold weather hits! 

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6 minutes ago, ProDave said:

Possibly.

 

When the ASHP is heating the tank, the water within it will be circulating by convection and mixing.  It will stop being heated when the temperature probe senses it has reached demand temperature.  Is there a lower thermostat pocket?  I found I got better results (more hot water) by putting the temperature probe in the lowest pocket which is about 1/3 the way up the tank.

I’ll have a look!

 

no, just the one halfway down 

Edited by MYLOUBYLOU

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you might need to go into the settings to see what the HW hysteresis is- what the cut-in *and* cut-out temperatures are. also does the tank have one immersion, or two?

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Just now, MYLOUBYLOU said:
Flow rate at 3 bar pressure 
24 l/min
 
according to the spec of shower head

May car can, according to the spec, do 113 MPH.

Best to measure it.

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34 minutes ago, MYLOUBYLOU said:
Flow rate at 3 bar pressure 
24 l/min
 
according to the spec of shower head

so in 10 minutes 240 litres of water?

 

Your gonna need a bigger tank...

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47 minutes ago, Marvin said:

so in 10 minutes 240 litres of water?

 

Your gonna need a bigger tank...

Seems a lot not that we spend that amount of time!

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Yes, well, of course, you wouldn't use only hot water either, but worth finding out how much water you are using.

 

My 1400mm high tank can go from 25C at the bottom to 60C at the top. 

Edited by Marvin
Clarification, hopefully.

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