What is an equipment map/envelope?
With a heat pump the temperature it can produce water at is dependent on the ambient temperature.
The maximum water temperature possible will decrease when the ambient temperature decreases, but also when the ambient temperature increases. The maximum temperature achievable and how much it will reduce with decrease/increase of ambient temperature varies greatly with different products.
All products have an operational map/envelope which lays out visually, the flow temperatures the heat pump can produce and at what ambient temperature it can do it:
Example Maps
The above equipment envelopes/maps are what we would consider to be “good”performance maps.
The map on the left is from a Euroklimat Heat Pump: It can provide maximum flow temperature of 70°C and can give this with ambient -10°C up to 20°C. It can give 65°C with ambient between -20 and +35
The Map on the right is for a Midea Heat Pump, it’s maximum flow temperature is 65°C, this can be achieved anywhere between -10°C and +37°C.
To demonstrate where it is possible to go wrong with performance envelopes/maps there are 2 more above:
When you look at the map above on the left: The maximum flow temperature this unit can provide is 55degrees, this can be achieved down to 0°C and as high as 25°C. As we usually design to minus 5°C in the UK, this unit can really only be applied with a flow temperature of 50°C as this is the maximum temperature achievable at -5°C.
This heat pump would not be suitable for DHW, it can’t do the temperature required for legionella at anytime and also does not guarantee operation once ambient is above 25°C.
The Map on the right has two lines, the lower is for the standard unit and the higher line is for the same range but with a special kit on it which increases the possible flow temperature. With the standard unit the maximum achievable flow temperature is 55degrees, this is available between +10°C and +20°C and so could not really be applied at thistemperature for UK heating or DHW. The maximum flow temperature achievable with a minus 5°C ambient is 50°C,this us possible from -5°C up to +35°C.
Make Sure The System will Start When It Is Cold
One crucial thing to notice in all of these maps, is that they do not show performance until +20 / +25, this means that the unit does not ensure proper performance until the water in the loop is above that temperature. Good heat pumps will still start with water at this temperature, they will run for a short period of time and then stop for short period of time, they will start and stop until the eater gets above this temperature. There are many heat pumps on the market which literally will not start if below this temperature – you need to know if this is the case or not – if being started in winter, you will require another heat source to heat the water above this temperature before the heat pump will start - perhaps an inline electrical heater?
Don't Get It Wrong
Checking a heat pumps performace map is of imperative importance, choose a heat pump for DHW that only works up to 25°C ambient and on the hottest day of the year, your hot water temperatures will not be achieved, design a heating system which requires 55°C FT and then find that it only does it down to 0°C and on the coldest day of the year the building will be cold........
Some heat pumps literally switch off and will not heat at all at around -5, these temeratures are rarely experienced, but will your client thank you if they have zero heating on the coldest day of the year?
Performance maps/evelopes are important, we put them in every proposal that we issue - if you are specifying equipment with another distibutor/manufactuer ask to see them, if they can't provide a map, don't specify the equipment!
