Air Source Heat Pump Heat Curve

Fatferds12

Hi - We have a Danfoss air source heat pump which was here when we moved in. I've read the manual but am still confused about how to set the heat curve and room temperature. Currently the room temp is 20C and heat curve 37C but isn't overly warm. Should I put the room temp up and heat curve down or just the room temp? I'm not sure what would be the most cost efficient. Thanks for any help.

matelodave

Perhaps a bit more info would help - like heatpump model, type of system (rads,underfloor, fan convectors). what stats have you got to control it (room stats or just a unit stat). If you've got a room stat what sort (basic or programmable) when do you run it, have you got it on a timer - if so when do you switch it on and off.

Is the heat curve weather compensated or fixed at 37 degrees. Weather compensated would adjust the flow temperature in accordance with the outside temperature, which means that it wont always be 37, whereas if it's not weather compensated then it should remain at 37

Generally if you've got a heatpump and it's running at a fairly low flow temperature then you need to keep it running for a lot longer than you would with a conventional boiler.

Turning up the flow temperature will increase your heating cost by about 2.5% for every degree above about 35 degrees. You should be careful that you don't crank it up to the point where the back-up heater kicks in (about 50 degrees) otherwise your cost will skyrocket.

In fact you really shouldn't let the place get stone cold because it will take a long time to get warm again (ours takes over a day to recover if we shut it off).

Ideally a programmable thermostat which allow you to set the temperature back a couple of degrees overnight (or during the day) is a lot better than trying to crank up the flow temperature to heat the place rapidly.

Fatferds12

Hi - It's a Danfoss DHP-AQ which supplies the underfloor heating and hot water. There's no separate stats other than what the unit is set at. I think the heat curve is weather compensated as the manual says the heating curve supply temp is calculated at 0c outdoor temperature. We have it on 24hrs as it takes a long time to heat up. I'm not sure how you adjust the flow temperature as there's no obvious setting or is that the heat curve? As you can tell I'm a bit new to this but thanks for your reply.

matelodave

Have you got the operating manual - try downloading it from Danfoss if you havent.

If you haven't got an external (room stat) or sensor then you'll have to try adjusting what controls you've got.

However don't go mad, only adjust one thing (either curve or room temp) at a time and give it a couple of days to see what effect it has. I'd also be tempted to read the electricity meter on a daily basis whilst you are doing it to see whether it has dramatic effect on your energy consumption - it would be good to get a few of day of readings before faffing around so you've got some idea of a reference (bear in mind that your consumption will vary anyway depending on the external temperature.

I'd try increasing the room temp to either 21 or 22 (although I dont know how the unit knows if it doesn't have an external sensor or stat). Has it got a time controller or does it try to maintain a constant temperature 24 hours a day?

I've had my 11kw Daikin ASHP for nearly 10 years now and I've worked out how to tweak some of the engineering settings from their factory settings. We've also got programmable stats that control the u/f heating loops in each room and switch the pump on an off according to demand. The heat curve on mine adjusts the flowto between 45degrees at -5 outside to 30 degrees when it's +20 outside which means that it can vary between 30 and 45 degrees but is usually around 35 (it used to be 40 at -5 but I've just upped it a bit to improve heating imes). I have the back up heater switched off so there's no possibility of it being inadvertently activated

The room stats are all set for a background temp of 17 degrees with an uplift to the rooms according to the time of day and their usage (ie bedrooms & bathroom when we get up and go to bed (7am-9am and 8pm-10pm), Lounge from when we get up and go to bed(7am to around 10pm), Study from 7am to 5pm, Kitchen around 8-9am, 12-2pm and 5-7pm.

However it can come on and off during the night so the house temperature does not fall below 17 (some nights it will run all night if it's cold outside). The rooms still take well over an hour or so to get up to temperature

It only heats water once a day in the mornings before we get up to 45 degrees (it gets a boost on Saturdays to 60 degrees to sterilise against Legionella)

It did take several months to figure it all out but generally we don't have to tweak it much at all now we've got it optimised.

However, the energy consumption in winter does look a bit alarming sometimes. We can use up to 50kwh in a day if it's everso cold outside. Our total leccy consumption in a year (we are all electric) is around 7000kw, 70% of which we use in the winter. Heating and hot water probably account for about 4000kw

Fatferds12

Thank you so much for this reply. I'll do as you say and change one thing at a time and monitor the meter. The people before us had it set very high as he felt the cold so we're just trying to get it back to 'normal'. I know adjusting the curve is a better way than the room temp but having always been a boiler/thermostat user this is all bit of a dark art! Thanks again and I'll see how it goes.

richardc1983

How are you getting on?

Your system will decide its flow temp based on the outdoor temp, the colder the outdoor temp the warmer the radiators will be.

If you want the house warmer, turn the temperature up that you want inside. So say from 20 to 21/22 this will keep the system running from longer.

Where is your thermostat that you set 20c located?

Fatferds12

Hi - Thanks for replying. My confusion with an air source heat pump (ashp) is the connection between the room temp and the heat curve temp. I've read that the heat curve should be as flat as possible and increasing the room temp by 1 degree increases the heat curve by 2 degrees. There isn't a separate thermostat and it's all set on the ashp. We don't have radiators but underfloor heating. Usage has been a bit less recently but then it's been warmer outside too. The manual isn't helpful so I'll probably just accept the fact it's more costly than I'm used to. Thanks again for replying.

richardc1983

I have read page 23 of the manual I believe is for your model. It states that the flow temp is dependant on the outdoor temperature... you can adjust this curve for -5c, 0c & +5c. Setting the temperature higher internally will not increase the flow temperature to increase the flow temp you will need to adjust the curve so that the flow temp is higher. What is it set at currently?

If you are wanting a higher temperature inside you will need to change the curve so that it responds with a higher flow temp to a not as cold outdoor temp. This will increase the running costs. You will also need to check that backup heater is not programmed to come on as well.

http://kesko-onninen-pim-resources-production.s3-website-eu-west-1.amazonaws.com/pimdocuments/DOC064186479136_IR.pdf

7.1 Tuning the heating system
To obtain a heating system balance and obtain an even and comfortable indoor temperature, the heating system may need adjustment
according to the example below.
The indoor temperature is adjusted by changing the heat curve. The heat curve calculates the supply temperature depending on the
outdoor temperature. The lower the outdoor temperature, the higher the supply temperature.
The heat curve may need to be adapted to obtain a pleasant indoor temperature in any weather conditions. A correctly set heat curve
reduces maintenance and gives an energy efficient operation.
See chapter CURVE for more information.
N
Adjust the heating system during the cold season to obtain the best possible performance.
N
Tuning must be carried out over a few days as the inertia in the heating system causes the indoor temperature to change slowly.
Tuning example
1. Choose one of the rooms, where the highest temperature is desired (20-21°C), as a reference room for the indoor temperature.
2. Place a thermometer in the room.
3. Open all radiator valves fully.
4. Leave the ROOM value set at 20°C.
See chapter ROOM for more information.
5. Note the temperature in the reference room regularly over a 24 hour period.
6. Adjust the ROOM value so that the reference room reaches your required indoor temperature of 20-21°C. Remember that other
rooms will have different temperatures during tuning, but these are adjusted later.
7. If the ROOM value must be adjusted more than 3°C upwards or downwards the CURVE value must be adjusted instead.
See chapter CURVE for more information.
8. If the indoor temperature varies several degrees despite tuning, a specific part of the heat curve may need adjusting. Check at what
outdoor temperature the variation is greatest and adjust the curve at the corresponding value (CURVE 5, CURVE 0, CURVE -5).
See chapter Adjusting the heat curve at -5°C, 0°C and 5°C for more information.
9. When the reference room has an even temperature of 20 - 21°C over a 24 hour period, you can adjust the radiator valves in the
other rooms so that their indoor temperatures are the same temperature or lower than the reference room.
7.2 CURVE
The most energy efficient and cost effective setting is achieved by changing the CURVE value to adjust the temperature in the house to
an even and constant temperature.
The control computer shows the value for CURVE by means of a graph in the display. The heat curve can be changed by adjusting the
CURVE value. The value for the CURVE indicates which value on the supply temperature is required in relation to the outdoor temperature

7.3 ROOM
If you wish to temporarily increase or reduce the indoor temperature, change the ROOM value. The difference between changing the
ROOM value and the CURVE value is as follows:
When changing the ROOM value, the angle of the curve on the system's heat curve does not change, instead the entire heat curve is
moved by 3°C for every degree change of the ROOM value.
The reason that the curve is adjusted 3°C is that an approximate 3°C increase in supply temperature is usually needed to increase the
indoor temperature 1°C.

7.4 Adjusting the CURVE at -5°C, 0°C and +5°C
Sometimes, at outdoor temperatures between -5°C and +5°C, part of the heat curve may need adjusting if the indoor temperature is not
constant. For this reason, the control system includes a function which only adjusts the heat curve at three outdoor temperatures: -5°C,
0°C and +5°C.
This function will allow one to increase or reduce the setpoint value for the supply line temperature, without affecting the rest of the
heat curve, at three specific outdoor temperatures. If, for example, the outdoor temperature is -5°C, the supply temperature will change
gradually between 0°C and -10°C, maximum adjustment being reached at -5°C.
The figure below shows the adjusted CURVE -5. The adjustment can be seen in the graph in the form of a bump. Choose to adjust the
heat curve individually at three specified outdoor temperatures: -5°C, 0°C and +5°C. The supply temperature can be changed by plus/
minus 5°C.

Fatferds12

Hi - thanks for this. The heat curve is set on 37 so I've turned it down to 36 to see what happens and kept the room temp at 20 degrees. The manual you've sent is slightly different to mine but describes the heat curve in a clearer way so thanks for that. Fingers crossed it helps but as you can see from the manual it isn't straight forward at all!

richardc1983

36 at what outdoor temp though?

Fatferds12

So this is where I fall down as I don't know where I would find out the outdoor temp setting so will have a look in the manual and let you know. The only 2 temps I think I can change are the room and heat curve................ Off to have a look