The right temperature of domestic hot water at the collection points is a key parameter to ensure user comfort. Various types of heating devices are used for this purpose, from standard electric water heaters to heating boilers, or in recent years, increasingly popular heat pumps cooperating with domestic hot water tanks.
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Basic types of DHW tanks
The basic function of domestic hot water tanks is to heat and store domestic hot water at the appropriate temperature and quality, with the lowest possible energy losses to the environment. Among the tanks available on the market, the following should be mentioned in particular:
- layered containers,
- water jacketed tanks,
- combined tanks (multivalent – so-called "tank in a tank"),
- tanks with heating coil, etc.
We will focus on the latter in the following article.
New series of NIBE-BIAWAR domestic hot water tanks for heat pumps
Analyzing recent years in terms of the choice of heat sources for heating buildings and preparing domestic hot water, we clearly notice that Investors are increasingly choosing heat pumps. When deciding to install a pump in our home, we must know that it requires, first of all, a different domestic hot water tank than, for example, a standard gas boiler. With heat pumps in mind, engineers from NIBE-BIAWAR have prepared a new series of domestic hot water tanks with a design dedicated to modern heat sources such as the aforementioned pumps.
But from the beginning.
How to choose the right capacity of the domestic hot water tank?
The basic criterion for ensuring the comfort of domestic hot water is the proper selection of the capacity of the domestic hot water tank, and in the case of heat pumps, such a selection looks a bit different than a few years ago and in the case of, for example, a gas boiler. Until now, we were not surprised by a set consisting of a domestic hot water tank with a capacity of 100-140 l, cooperating with a 24 kW gas boiler and supplying a family of 4-5 people with domestic hot water. In the case of such a solution, we used the small storage capacity of the tank and the so-called permanent efficiency of the boiler in combination with a high domestic hot water temperature. The main role here was played by the gas boiler, which could operate with high heating power and high supply temperature (>80°C).
In the case of heat pumps, the situation is completely different, which is primarily due to certain differences in relation to devices burning fossil fuels. This mainly concerns the lower maximum supply temperature of the heat pump, which in turn translates into a lower temperature of domestic hot water. And this is the crux of the matter - because of the lower temperature of the heat pump heating medium, we need a larger heat exchange surface and, consequently, a larger tank capacity for the same 4-5-person family.
Taking into account the above-mentioned assumptions and the needs of heat pump users in terms of domestic hot water supply, a new series of NIBE-BIAWAR WE 220.81 PC domestic hot water tanks and NIBE-BIAWAR WE 300.81 PC2 domestic hot water tanks were created (with storage capacities of 207 and 285 l, respectively).
How are the new DHW tanks from NIBE-BIAWAR constructed?
The construction of the new containers is shown in Figure 1, and below we present the individual elements influencing the advantages of the mentioned devices.
Fig. 1. Construction of WE 220.81 PC and WE 300.81 PC2 tanks.
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Capacity of NIBE-BIAWAR tanks
What should the actual capacity of the tank be and what does it depend on? The key factor here is the number of users in a given building, the temperature and the required comfort/amount of domestic hot water. It is assumed that for comfortable use of water without having to wait for it to be heated, about 40-60 l per day per resident is needed. It is therefore easy to calculate that the presented tanks will be enough for 4 to even 7 people. However, it all depends on the individual needs of the household members.
Tank coil surface
As mentioned earlier, due to the lower power supply parameter of heat pumps compared to boilers for solid and liquid fuels, a larger exchange surface (coil) is required. It has become a standard to assume about 0.25 - 0.3 m2 for every 1 kW of heat pump power. Of course, everything depends on the parameters and logic of work on domestic hot water, but the presented devices with coils with surfaces of 1.8 and 2.7 m2, respectively, perfectly fit the requirements of heat pumps for most home (and not only) heating devices.
Compatibility tables presented in technical materials or on nibe.pl are also helpful.
Connector for heater mounting
A very important element is the connector for mounting the electric heater, which is especially important to remember in the case of cooperation with a heat pump. The heater itself in the tank will perform several very important functions, where the two basic ones are:
- possibility of periodic overheating (so-called thermal disinfection),
- the heater can support domestic hot water heating in times of high demand for domestic hot water.
An additional advantage is the low-positioned heater, which ensures heating of almost the entire volume of the tank.
Temperature sensor covers and thermal insulation
Another very important element that is often overlooked is the temperature sensor/sensor covers. The presented devices have three locations at different heights, which allow for individual setting of the level from which the domestic hot water heating will begin. It should also be mentioned that even the lowest sensor cover is located above the heater connector, thanks to which the heater will always be under the supervision of the heat pump control automation.
Like most NIBE -BIAWAR devices, they also have a removable casing and thermal insulation, which allows the device to be transported in difficult conditions without the risk of damage.
The table below presents the technical data of the containers described in the article.
Table 1. Technical data of WE 220.81 PC and WE 300.81 PC2 tanks.
Parameter | Unit | Container model | ||
WE 220.81 PC | WE 300.81 PC2 | |||
Energy efficiency class* | - | C | C | |
Storage capacity (V)* | l | 207 | 285 | |
Standing Loss (S)* | IN | 76 | 96 | |
Coil heating surface | m2 | 1.8 | 2.7 | |
Maximum tank operating temperature | °C | 85 | ||
Maximum allowable instantaneous temperature in the tank | °C | 98 | ||
Maximum coil operating temperature | °C | 110 | ||
Maximum tank operating pressure | bar | 6 | ||
Maximum coil operating pressure | bar | 16 | ||
Coil power** | 70/10/45°C | kW | 37.0 | 53.9 |
Coil efficiency** | 70/10/45°C | l/h | 912 | 1288 |
Connection of electric heating module | 1 ½” GW | |||
Anti-corrosion protection | Ceramic enamel + magnesium anode | |||
Magnesium anode dimension | mm/inch | ø21x1050 / ¾” | ø26x900 / 1” | |
Mass | kg | 89 | 116 | |
* In accordance with EU Regulation No. 812/2013, 814/2013.
** At a heating medium flow rate of 2.5 m3/h and a heating medium temperature of 70°C, supply water temperature of 10°C and utility water temperature of 45°C.
All the above-mentioned features of the WE 220.81 PC and WE 300.81 PC2 tanks make them ideal solutions for cooperation with heat pumps from various manufacturers (not only NIBE- BIAWAR ) and perfectly complement our offer of devices for domestic hot water preparation.